Other DNA Evidence

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Following the murder, the Scientific Police undertook technical inspections of:

  • Meredith's cottage at 7, Via della Pergola (on November 2-4, 2007)
  • Sollecito's Audi A3 car (November 13, 2007)
  • Sollecito's apartment in Corso Garibaldi (November 13, 2007)
  • Le Chic pub, run by Patrick Lumumba, who was initially a suspect, owing to Knox's false accusation. (November 14, 2007)
  • Guede's apartment in Via del Canerino (November 20, 2007)
  • A further inspection at 7, Via della Pergola (December 18, 2007)[1]

This is a summary of their findings.


7, Via della Pergola

The small bathroom

"The small bathroom"
The small bathroom


The small bathroom was immediately adjacent to Meredith's bedroom. The picture, right, shows a view into the bathroom, with Meredith's doorway just visible to the left.

  • Drops of Meredith's blood were found in 4 places: on the light switch, the toilet seat cover, the door, and the bathmat.
  • Knox's blood was found on the tap of the wash basin.
  • A mixture of the two women's DNA (probably mixed blood) was found in three places: on the cotton bud box, the side of basin, and the bidet.
  • No trace of Guede's DNA was found in the small bathroom.
  • None of Sollecito's DNA was found, although a footprint matching his foot was on the bathmat.

The mixed traces are probably mixed blood because of the similar heights of the DNA peaks attributable attributable to Meredith and Knox (see below).

At Knox and Sollecito's trial, Judge Massei considered this evidence and concluded:

The mixed trace specimens found in the sink and in the bidet and on the box of cotton buds therefore signify that Amanda, soiled with Meredith’s blood, entered the bathroom which was right next door to the room in which Meredith had been stabbed; putting her hand against the door she left a mark on it and the dribble of blood which remained is a sign [proof] of this, and left a mark also - still with Meredith’s blood - on the light switch; she touched the cotton-bud box which was on the sink and left a mixed trace specimen of herself and of Meredith; to clean her hands she used the sink in which, through the act of scrubbing, she left her own biological trace mixed with that of Meredith, and used the bidet, most likely to wash her feet, which must have become *blood+ stained in Meredith’s room, where there were widespread and abundant traces of blood even on the floor, and where the blood was spattered over various parts of the room, and also in the bidet [303] she left a trace specimen of what appeared to be diluted blood, which contained both her own DNA and that of Meredith.[2]

The light switch

"Blood stained light switch"
The light switch
Rep. 23 is stain of apparently diluted blood in the light switch in the small bathroom. A visible mark can be seen on the right hand switch and on the left of the supporting plate. This tested positive for human blood. The DNA matched the profile of Meredith.[3]

The bidet

"Blood stain in bidet"
Blood stain in the bidet
Rep. 66 is a smear of blood, beside the plughole of the bidet. It has the visual appearance of dilute blood and tested positive for human blood in a scientific test. DNA testing revealed that it is a mixed profile of Knox and Meredith.[4]

The wash-basin

"Washbasin in the small bathroom"
The wash basin
Rep.136 is a sample taken from a visible smear on box of cotton buds beside the tap on the basin. It tested positive for human blood. DNA testing revealed a mixed profile of Knox and Meredith.[5] In the electropherogram, the peaks attributable to the two women are of similar heights, implying similar concentrations of DNA from both women in the sample. Blood is extremely rich in DNA, so this is definitely not a sample of "blood DNA" from one woman and "touch DNA" from the other. It is very likely to be a mixture of Knox's and Meredith's blood.

Rep. 137 is a sample taken from the left hand side of the wash-basin. It tested positive for human blood and DNA testing revealed a mixed profile of Knox and Meredith. Again, the similarity of the heights of the electropherogram peaks suggest a probable mixed blood sample.[6]

"Tap on washbasin in the small bathroom"
The tap smeared with Knox's blood
Rep. 24 is a sample taken from the tap on the basin, where there are visible smears of blood. This sample tested positive for human blood and matched the DNA profile of Knox. There are no DNA peaks attributable to Meredith, so there is no doubt that the smears on the tap are Knox's blood.[7]

The toilet

"Blood sample on the lid of the toilet"
The toilet seat cover
Rep. 139 is a sample from a visible smear at the back of the toilet seat cover. It tested positive for human blood and the DNA test matched Meredith.[8]

The door

"Blood drip on door of the small bathroom"
Blood trace on the door
Rep. 140 is a visible streak of blood (probably diluted) on the edge of the door into the small bathroom. It tested positive for human blood and the DNA test matched Meredith.[9]

The blue bathmat

See The Bathmat Footprint

Rep. 22 is from a stain in dilute blood, in the shape of a bare foot, on the bathmat. The stain tested positive for human blood and matched the DNA profile of Meredith.[10] The footprint matches the foot of Sollecito but not Knox or Guede.

Negative results

Further samples were taken from the small bathroom but proved negative:[11]

  • Rep. 138 from the wash basin.
  • Rep. 141 from the waste water pipe.

Significance of the mixed DNA samples

A striking example is the mixed DNA profile from the sample taken from the cotton bud box on the basin. The following figure shows the electropherogram analysis of the DNA profile, alongside reference profiles from Knox and Meredith.

"Electropherogram of mixed DNA samples"
Comparison of mixed DNA profile, taken from cotton bud box, with reference profiles of Knox and Meredith. Source: Dr. Stefanoni's presentation

All the peaks in the sample (left hand trace) are accounted for by peaks from either Merdith's (center) or Knox's (right) profiles, with some being common to both women. We have marked the peaks with a green spot for a Meredith match and a red spot for a Knox match, with a half-and-half spot indicating that the particular peak is common to both women's DNA.

The trace tested positive for human blood, so there is no doubt that there is the blood of at least one of the two women in the sample, but is it the mixed blood of both? The heights of the peaks give some indication of the concentration of DNA in a particular sample and, here, the peaks for the two women are very similar, with some of Knox's exceeding the height of Meredith's. Blood is a very rich source of DNA and the equivalence of the two contributors to the mixed trace would certainly be accounted for if the trace is indeed mixed blood. Luciano Garafano, in Darkness Descending stated:

However, here is the electropherogram and you can see that the RFU value is very high, so the sample is undoubtedly blood, which is the body fluid that provides the greatest amount of DNA. In some cases you see higher peaks of Amanda’s DNA than Meredith’s. Amanda has been bleeding.[12]

This and the other mixed traces in the small bathroom are definitely not "touch DNA" of one of the women, mixed with "blood DNA" of the other. Touch DNA results in minute amounts of DNA being deposited, compared with that in blood.[13]

Knox's court testimony gave one possible reason for how these mixed traces could have arisen. She said:

I went into the bathroom. I had these earrings, I had a lot of them, I like earrings, I had had them pierced recently, and I always had to wash them carefully because one was a little infected, and I had to take the earrings out and clean the ear, and that's when I saw some drops of blood on the sink. At first I thought they had come from my ears. But then when I scratched the drops a bit, I saw they were all dry, and I thought "That's weird. Oh well, I'll take my shower."

So could the mixed traces be accounted for by drops of blood from Knox's ear mixing with traces of Meredith's blood? Apart from the fact that Knox herself testified that the blood was dried, we have to consider the matter of probability. For this to be true, we would have to believe that the murderers had left 7 traces of Meredith's blood; then, about 12 hours later, Knox would have arrived and dropped four drops of her own blood: one hitting the tap, one landing precisely on the spot of Meredith's blood on the side of the basin, one landing precisely on the drop of Meredith's blood on the cotton bud box, and the other landing exactly on the drop of Meredith's blood in the bidet.

No other specific explanation of these mixed traces has been given by the defense.

Judge Massei's report took the view that the mixed traces were not mixed blood. He said:

Amanda was not wounded; in the days following no one spoke of wounds that she might have had; the examination which was carried out on her when measures restricting her personal freedom were taken ruled out the presence of wounds. Meredith’s situation was the complete opposite. In relation to this and to the circumstance by which haematological stains attributable to Meredith were found on the inside of the door, on the toilet-seat cover, on the light switch, it should be deduced that the haematological components found in the sink, in the bidet, on the box of cotton buds were also from Meredith. Nor can it otherwise be argued for the presence of a drop of Amanda’s blood on the tap of the sink. This consisted of a spot of coagulated blood, with respect to which Amanda explained that it came from her own ear having been pierced; this spot, furthermore, was located towards the inside of the sink: distinct, separate and morphologically different, therefore, from the trace found in the sink itself.[14]

However, the panel of judges may not have been unanimous on this point. According to Barbie Nadeau:

The defense’s other biggest mistake, according to interviews with jurors after the trial, was doing nothing to refute the mixed-blood evidence beyond noting that it is common to find mingled DNA when two people live in the same house.[15]

The additional experts, Conti and Vecchiotti, appointed by the Hellmann appeal, were not asked to re-examine the mixed DNA traces. No further facts on this matter have been offered since the Massei trial.

Meredith's bedroom


"Meredith's bedroom"
Meredith's bedroom
More than 90 samples were taken from Meredith's body and from items in her bedroom. Many of these tested positive for Meredith's blood, which is unsurprising. The major points of note are:
  • One of the vaginal swabs tested positive for Guede's DNA (but not for semen).
  • A small bloodstain on the outside of Meredith's brown leather handbag tested positive for Guede's DNA.
  • A trace of Guede's DNA was found on the cuff of Meredith's blue sweatshirt.
  • A trace of Sollecito's DNA was found on Meredith's bra clasp.
  • Knox's DNA was not found in the room.

Meredith's body

A number of swabs were taken from Meredith's body and tested for DNA.

  • Reps. 12A/B/C were vaginal swabs, all of which matched Meredith's DNA. One of them (Rep. 12B) included a mix of Guede's DNA. It tested negative for semen.
  • Reps. 13A/B/C were rectal swabs. All of them tested positive for Meredith's DNA.
  • Rep. 14 was from 7 textile fibers (probably wool). They tested negative for DNA.
  • Reps. 15/A/B/C/D/E and 16A/B/C/D/E were samples taken from beneath each of Meredith's fingernails. The DNA matched Meredith.
  • Rep. 21 was taken from the blood at the site of Meredith's wound. It was used as the reference sample for Meredith's DNA.

Meredith's brown leather handbag

"Meredith's handbag"
Meredith's handbag
Rep. 166A/B were two samples taken from the handbag, where there is a small stain visible in the center right of the accompanying picture. The traces tested positive for human blood and were a match for Guede and Meredith.[16]

Another trace (Rep. 201) taken from a different point on the bag yielded a negative result.[17]

Meredith's bra

Reps. 59A/B/C/D/E/F were six samples taken from Meredith's heavily blood-stained bra. All tested positive for Meredith's blood. One of them (Rep. 59B) included a mix of Guede's DNA.

The bra clasp

See The Bra Clasp

Rep. 165A/B were two samples taken from the clasp of Meredith's bra, which had been cut or torn from the main part of the garment, and was found on the floor of her bedroom. Trace 165A matched the DNA of Meredith, but Rep. 165B was a mixed trace which matched Sollecito and Meredith.[18]

The light blue sweatshirt

Meredith had been wearing a light blue sweatshirt at the time of the attack. Rep. 171A/B/C were three samples taken from this heavily blood-stained garment. Rep. 171/B taken from the right cuff of the sweatshirt was a mixed DNA trace, matching Guede and Meredith.[19]

Other samples

Other samples taken from Meredith's room matched just Meredith's DNA (unsurprising, given the amount of blood spread around the room) or were either negative. These were

  • Rep. 27 from a glass beaker (Meredith).
  • Reps. 60A/B/C/D/E from a green towel (negative).
  • Reps. 61A/B from a light-colored towel (Meredith's blood).
  • Reps. 62A/B/C/D/E/F from a beige towel (Meredith's blood).
  • Reps. 63A/B/C/D/E from a white sheet (Meredith's blood/negative)
  • Reps. 64A/B/C/D from tissues and a cotton wool ball. (Meredith's blood/negative)
  • Rep. 65 from the wall near the door (Meredith's blood).
  • Rep. 111 from an unknown gummy substance of white color (negative).
  • Rep. 114 from Meredith's slip (Meredith).
  • Reps. 115A/B/C/D/E/F/G/H/I/L from Meredith's blue jeans which she was wearing on the evening of the murder (Meredith's blood).
  • Reps. 116A/B/C from a toilet roll (negative).
  • Rep. 117, 118 and 135 from the floor (Meredith's blood).
  • Reps. 123 and 124 from the mattress (Meredith's blood).
  • Rep. 125 from the wall by the bed (Meredith's blood).
  • Rep. 126 from the interior door handle (Meredith's blood).
  • Rep. 127 from the door, near the lock (Meredith's blood).
  • Rep. 128 from the door lock fitting (Meredith's blood).
  • Rep. 129 from the wardrobe (Meredith's blood).
  • Reps. 185A/B/C/D/E/F/G/H/I from Meredith's beige duvet (4 negative; 5 Meredith's blood).
  • Reps. 164A/B from the wall, near the door (negative).
  • Reps. 167A/B/C and 170A/B/C from a pair of light colored socks (Meredith's blood).
  • Reps. 202A/B/C from a beige fabric handbag (Meredith's blood).

Knox's bedroom and personal effects

"Knox's bedroom"
Knox's bedroom

Samples were taken from:

  • Rep. 172: A stain on Knox's pillowcase.
  • Rep. 173A/B: A pair of socks.
  • Rep. 174: The floor, by the bed.
  • Rep. 175: The wall above the headboard of the bed.

These all tested negative for blood and DNA.

  • Rep.109/A/B/C/D/E were 5 samples taken from a pair of "Sketchers" shoes. All were negative for blood and just one of the 5 had a DNA profile: it was a match for Knox.
  • Rep.110/A/B/C were 3 samples from a multicolour handbag. They were negative for blood but all had testable DNA profiles which matched Knox.[20]

Overall, no evidence arose from these tests. The only point of note is how little DNA is left by a person in their bedroom and on their personal effects.

The large bathroom

"The large bathroom"
The large bathroom
The large bathroom, used principally by Filomena and Laura, was in two parts. The outer area is a kind of utility room, with a sink, washing machine and the hot water boiler. These two women's hair styling materials were there, including the hair dryer (and the socket where it plugged in) and a wall-mounted mirror. The inner part, separated by a door, comprised the bath, toilet, bidet and wash basin.

The toilet contained unflushed feces and toilet paper. In fact Knox had supposedly seen these while drying her hair in the outer part of the bathroom. Feces are unlikely to yield testable DNA, but Rep. 25 from the toilet paper matched the profile of Guede.

Rep. 26 was taken from the feces in the toilet but tested negative for DNA.[21]

Rep. 57A/B/C were taken from the wet towels found in the washing machine. The DNA test was negative.

Rep. 223 was taken from the hair dryer. The DNA test was negative.

Filomena Romanelli's bedroom

See Luminol Traces for details of the footprints found in Filomena's room
  • Rep. 198 from the lower left window frame: negative.
  • Rep. 199 from the window shutter: negative.
  • Rep. 169 from the pieces of the rock that broke the window: negative.

Living room/kitchen

"Ashtray in the shared living room"
Ashtray in the shared living room

Ash tray

Rep. 145 was a sample taken from a cigarette butt in the blue ashtray, on the table in the living room/kitchen. The mixed DNA profile matched Knox and Sollecito.[22]

This was the only trace of Sollecito's DNA found in any of the rooms in the cottage, apart from the trace found on the bra clasp in Meredith's bedroom.

Reps. 142, 143, 144, 146 and 147 were taken from five other cigarette butts. Three matched the DNA of an unnamed man ("man 7") and two matched an unnamed woman ("woman 3").

The floor

Reps. 186, 187, 188, 189, 190 and 191 were samples taken from different parts of the floor of the living room/kitchen. All tested positive for blood and Reps. 185-190 matched the DNA profile of Meredith. Rep. 191 yielded no identifiable profile.

Sollecito's Audi A3 car

Fifteen samples were taken from Sollecito's car (Reps. 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 78, 79 and 80A/B). In all cases, the genetic tests were negative and no DNA profiles were found.

Sollecito's apartment

The Double DNA Knife

See The Double DNA Knife
"Sollecito's knife drawer"
Sollecito's knife drawer
Police seized a kitchen knife from Sollecito's knife drawer, shown, right, after the removal of the knife. It is clear that no other items in the drawer look like possible murder weapons. This explains some people's surprise that the police tested that particular knife.

Rep. 36/A/B/C/D/E/F/G were six samples taken from the knife: 36A, D and F were taken from the handle; B, C and G from the blade. Trace 36A matched the DNA of Knox and 36B matched Meredith. Neither tested positive for blood. The remaining samples were negative.[23]

Other knives

"Sollecito's Brian Tighe design knife"
Sollecito's Brian Tighe design knife
See Sollecito's Knives

Rep. 33A/B/C/D were four samples taken from a black-handled folding knife. It tested negative for blood, but, in one sample, the DNA profile matched a mix of Knox and Sollecito. The other samples were negative.[24]

Other DNA traces

The Scientific Police took over 90 further samples from Sollecito's apartment and his personal effects. These were either negative for DNA or they matched Sollecito, Knox or a mixture of the two of them.

Guede's apartment

  • Rep. 58 was from Guede's toothbrush, in his bathroom. This was used as the reference DNA profile for Guede.[25] Contrary to some accounts, the police did not have Guede's DNA on file.
  • Rep. 148A/B/C/D were samples from a towel in Guede's bathroom. They tested positive for blood and matched Guede's DNA.
  • Rep 149 was from a plastic filter in the drain of the basin. It tested positive for blood and matched Guede's DNA.
  • Rep. 150A/B/C were samples from a pair of "Loose-fit" jeans. They were negative for blood, but two of the samples matched Guede's DNA.
  • Rep.151A/B were two samples from an entry ticket for the "Wonders of Chagall" exhibition. They tested positive for blood, and matched Guede's DNA.
  • Rep. 136 was a sample, presumed to be blood on the floor, beneath the basin. This tested positive for Guede's DNA.
  • Rep. 203 was a sample from a yellow hooded pullover. It was a biological substance, matching Guede's DNA.
  • Rep. 206 was from a long-sleeved "Timberland" top. It was a biological substance, matching Guede's DNA.
  • Rep. 208 was from a pair of white jeans. It was non-blood and matched Guede's DNA.
  • Rep. 210A/B were two traces froma pair of "Mecca" jeans. One tested positive for Guede's (non-blood) DNA. The other was negative.
  • Rep. 211 was from a light beige pullover. It tested positive for Guede's (non-blood) DNA.
  • Rep. 215 was a small towel and toothbrush. The trace was presumed epithelial cells and tested positive for Guede's DNA.

A further 17 samples from Guede's apartment and his personal effects were negative for blood and DNA.


  1. Dr.ssa Patrizia Stefanoni, Direttore Tecnico Principale Biologo della Polizia di Stato: Accertamenti tecnici di natura biologica, presentation to Massei Court. pp.23-25
  2. Massei translation, p.281
  3. Stefanoni: pp.93-94
  4. Stefanoni: pp.112-113
  5. Stefanoni: pp.114-115
  6. Stefanoni: pp.116-117
  7. Stefanoni: pp.95-96
  8. Stefanoni: pp.118-119
  9. Stefanoni: pp.120-121
  10. Stefanoni: pp.90-92
  11. Stefanoni: p.49
  12. Luciano Garafano, Darkness Descending, page 371
  13. See, for example, UK Crown Prosecution Service: Low Copy Number DNA testing in the Criminal Justice System (''Low Copy Number DNA testing in the Criminal Justice System''. This states that the smallest bloodstain visible with the naked eye contains 50 - 100 cells—the blood stains in the small bathroom were all easily visible. By comparison, it says that the amount of DNA left on a cup by drinking from it might be just 5 - 10 cells.
  14. Massei translation, p.280
  15. Barbie Nadeau, Angel Face, page 152
  16. Stefanoni: pp.127-128
  17. Stefanoni: p.45
  18. Stefanoni: pp. 124-126
  19. Stefanoni: pp.129-130
  20. Stefanoni, p.53
  21. Stefanoni: p. 51
  22. Stefanoni: pp.122-123
  23. Stefanoni: pp. 105-106
  24. Stefanoni: pp. 103-104
  25. Stefanoni, p.108-109