Luminol Traces

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On December 18, 2007 Deputy Commissioner Maurizio Arnone and Chief Inspector Claudio Ippolito went to the cottage to spray luminol on certain areas and photograph any traces of blood that the luminol might reveal.[1] The areas that were to be covered included the kitchen-living room, the bedrooms of Amanda Knox and Filomena Romanelli, and the large bathroom.[2] They discovered seven footprints in the corridor between Meredith's bedroom where she was murdered and Amanda Knox's bedroom. No similar footprints were discovered anywhere else in the cottage. [3] The three footprints in Knox's room yielded Knox's genetic profile and one of the footprints in the hallway contained both Amanda and Meredith's DNA.[4]

Luminol Before After.jpg

Footprints Found To Match Amanda Knox and Raffaele Sollecito

Dr Rinaldi and Chief Inspector Boemia were given the task of doing the technical investigation of the footprints that the luminol revealed.[5] Of these three had sufficient details to be used for the purpose of identification. Two of the footprints made in blood were identified as being compatible with Amanda Knox and the third was identified as being compatible with Raffaele Sollecito.[6] It was further possible to use the same measurements to exclude the possibility that Rudy Guede made the bloody footprints.[7]

Finding 1 / L5 / Rep. 180

Located in the bedroom of Amanda Knox this was identified as the right foot most likely in a deposit of haematic substance. The 1st toe, 3rd toe, the metatarsus, and a portion of the plantar arch led the technicians to conclude that the footprint was compatible with Amanda Knox's right foot.[8] This trace was also found to have Amanda Knox's DNA.[9]
Map of Luminol Traces in Cottage, Mixed DNA in green -- Click for full size

Finding 2 / L7 / Rep. 181

(Pictured above) Located in the corridor in the direction facing the exit was the print of another right foot made imprinted by a deposit of blood.[10] Next to the right foot was a print (L6) made by a left foot but there were no useful details for identification purposes.[11] The right foot did provide useful information. Being placed on a Robbins grid the investigators were able to get measurements for the big toe, both width and length for the metatarsus, and a width measurement for the heel.[12] The bloody footprint was determined to be compatible with Raffaele Sollecito's right foot.[13]

Finding 7 / L9 / Rep. 184

Located in the corridor directly in front of the door to Meredith Kercher's room and pointing towards the entrance as if entering the room.[14] Measurements for the big toe, metatarsus, and heel were found to be compatible with Amanda Knox's foot.[15]

Mixed DNA (Finding 6 / L8 / Rep. 183)

The discovery of Amanda Knox's DNA mixed with the victims DNA in a footprint with no useful characteristics that is presumed to have been made in blood is difficult to explain.[16] Despite claims to the contrary there is no usable DNA in dust.[17] The defense maintains that there is no way to date when the DNA was deposited which is true but any argument based on this requires that we assume Amanda Knox was walking around making footprints in her own blood prior to the murder. If something like that happened you would expect a reference to a specific event which could then be verified or denied by the other two roommates. This line of argument would also run into problems in explaining why a foot compatible with Raffaele's foot was also making imprints in blood.

Knox attempted to create an opening for how this finding could be innocently explained, but it is hard to believe. She claims that when she discovered that all the towels in the bathroom were missing she decided to use the bloody bathmat as a sliding surface to return to her room. She claims that she remembers her foot sliding off the bathmat and that could be how she got Meredith's blood mixed with her DNA. This comes across as absurd. Why would someone use a bloody bathmat to slide on back to her bedroom rather than just walking? Knox is lying in an effort to explain this DNA evidence in much the same way as Sollecito lied to explain the DNA on the knife. You are left asking yourself would someone uninvolved with the murder be so quick to make up lies in an effort to explain evidence against them?

Reps 176 and 177 in Filomena's Room

Rep 176 - Meredith's blood tracked to the site of the staged burglary
Rep 177 - Knox DNA mixed with Meredith's blood in Filomena's room

Rep 176 (L1 in the inspection report) was a Luminol trace found to have the victim's DNA, located on the floor near the window..[18] Rep 177 (L2) was between the door and the window, containing a Knox/Victim mixed profile.[19] That the victim's blood had been tracked into Filomena's room proved to the satisfaction of the courts that the staging must therefore have taken place after the murder.

More on the staged burglary can be found here

False Positives and Luminol

A popular rebuttal against the claim that the footprints were made in blood is that luminol also fluoresces when sprayed on a few substances other than blood. The reason that luminol is useful to crime scene reconstruction rests on the fact that the substances that cause false positives are typically not found at crime scenes and in the cases of substances such as some brands of enamel paint the false positive are easy to detect because the reaction is not limited to a blood deposit pattern but covers the entire affected surface. In our case the luminol reactions were in the shape of feet with three of the traces having succinct details to identify them as footprints compatible with Amanda Knox and Raffaele Sollecito. The footprints were also limited to the part of the corridor between Meredith and Amanda's room and were not found anywhere else in the cottage. This would allow us to eliminate reactions to paint, terracotta or ceramic elements in the tile.

To claim the footprints are the result of a false positive one is limited to claiming it is something that was on the feet of Knox and Sollecito. The most common and potentially exculpatory explanation would be bleach. If bleach was used in the cleaning of the bathroom Amanda Knox could have gotten it on her feet and then made imprints that would react to luminol. This fails when one considers that the luminol was applied December 18[20] and the murder happened November 1st with the body discovered November 2nd. Bleach only causes a reaction with luminol for a few days after the bleach is deposited.[21][22] After a few days the hypochlorite evaporates and so nothing is left to cause Luminol to emit light. Since in this case six weeks had passed it is impossible to attribute the chemiluminescence to bleach.

With bleach eliminated the last remaining possibility would be a vegetable peroxidase. Turnip, parsnip, and horseradish pulp would give the strongest reaction but carrot or onion pulp would also work.[23] The defense is free to argue that Knox and Sollecito were in the habit of applying turnip pulp to their feet but no one is required to believe that claim and, importantly, they did not testify in court regarding any such practice. The unbelievability of the argument is the reason Knox supporters limit their argument for false positives to generic substances causing luminol to react. If they made the argument with any of the possible substances it would sound ridiculous. The elimination of bleach as a possible explanation for a false positive results in the only possible conclusion being that these footprints were made in blood.

In Judge Massei's analysis of the luminol evidence, the court observed that there was an abundant quantity of Meredith’s blood on the floor of the bedroom to be tracked around the house, but no other obvious source of luminol-reactive substances.[24] The fact that DNA testing revealed the presence of genetic material in the samples indicated to the Court the presence of biological material that reacts with luminol. The court said that attributing the fluorescence to fruit juice, rust, bleach, vegetables, etc., could not explain the presence of reactive trace in so many parts of the house, whereas the walking in blood and subsequent cleanup easily accounts for the findings.[25] The court took note of the defense experts' arguments that the footprints could have been in some substance, such as fruit juice, rather than blood, but noted that these arguments were hypothetical, and were not supported by any evidence or testimony relating to the spilling of fruit juice.[26]

Negative TMB Test

A final objection to the footprints that were revealed being blood is based on the negative results of TMB tests on the same surface, an event which happens on valid blood Luminol hits about half the time, according to Stefanoni[27]. Tetramethylbenzidine (TMB) is another presumptive test for the presence of blood. The problem with this argument is that TMB is only able to detect blood to a sensitivity of 1 in 10,000 parts.[28] Luminol on the other hand is extremely sensitive and is capable of detecting blood to a sensitivity of 1 in 1,000,000 parts on the low end and 1 in 100,000,000 parts on the high end.[29] That means that luminol is at a minimum 100 times the sensitivity of TMB and can be as high as 10,000 times the sensitivity. Attempting to compare the sensitivity of these two tests it is clear that luminol is by far the more sensitive test. Using a considerably less sensitive test to argue that the positive result of the test with a much greater sensitivity is a false positive is illogical and incorrect. [30]


The luminol traces are very strong evidence of Amanda Knox and Raffaele Sollecito's involvement in the murder of Meredith Kercher. The footprints establish that someone other than Rudy Guede was present and that these individuals had feet that are compatible with Knox and Sollecito. Attempts to explain the evidence by making reference to DNA in dust and to luminol false positives are at best misinformed and most likely intentionally deceptive. The argument that because TMB was used and the result was negative we should exclude the luminol results is wrong. The footprints are made in blood, they belong to Amanda Knox and Raffaele Sollecito, and they establish without a doubt that the couple was involved with the murder.


  1. Massei report translation, p.344
  2. Massei report translation, p.344
  3. Massei report translation, pp.344-349
  4. Exhibit 183 - Massei report translation, p.194,Massei report translation, p.380, and Hellmann report translation, p.69
  5. Their report is available in Italian Rinaldi & Boemia Technical Report -- Italian but we will source the English translation of the Massei report as much as possible.Massei report translation, p.346
  6. Massei report translation, p.349
  7. Massei report translation, p.349
  8. Massei report translation, p.347
  9. Dr. Stefanoni's Technical Assessment of Biologicals page 134
  10. Massei report translation, p.347
  11. Massei report translation, p.347
  12. Massei report translation, p.347
  13. Massei report translation, p.347
  14. Massei report translation, p.347
  15. Massei report translation, p.347
  16. Dr. Stefanoni's Technical Assessment of Biologicals Page 136
  17. Toothman, M et al."Characterization of human DNA in environmental samples" Forensic Science International Vol 178(1) p7-15
  18. Dr. Stefanoni's Technical Assessment of Biologicals page 131
  19. Dr. Stefanoni's Technical Assessment of Biologicals page 132
  20. Massei report translation, p.344
  21. Creamer, J. I., Quickenden, T. I., Crichton, L. B., Robertson P. and Ruhayel1,R. A., Attempted cleaning of bloodstains and its effect on the forensic luminol test. Luminescence, 2005 20:411 - 413
  22. Kent, E.J., Elliot, D.A. and Miskelly, G.M., Inhibition of bleach-induced Luminol chemiluminescence. J Forensic Sci, 2003 Jan;48(1):64 - 7
  23. Quickenden, T.I. and Creamer, J.I "A Study of common interferences with the forensic luminol test for blood" Luminescence 2001;16:295–298
  24. Massei Report Translation, p279
  25. Massei Report Translation, pp.283-285
  26. Massei Report Translation, p.285
  27. Massei pg 258
  28. NTSTC "Biological Screening Workshop: Blood" p58
  29. NTSTC "Biological Screening Workshop: Blood" p51
  30. In addition to the vastly different degrees of sensitivity the test for blood using luminol is applied directly to the surface being tested. A TMB test on the other hand involves swabbing the area and then testing the swab. This impacts the results in two ways. First, it lowers the relative sensitivity of TMB on uneven or porous surfaces like we have here. Even if there is sufficient blood remaining on the surface for a positive TMB result if the swab is prevented from making contact with the blood by the uneven surface then it will test negative. Luminol as a liquid that is applied directly to the surface does not have these limitations. The direct application of luminol to the area while beneficial for the sensitivity of that particular test it nevertheless has a destructive result. Luminol is a liquid being applied to the surface which will naturally lead to dilution. This will make it harder for TMB to detect the presence of blood and even more so in this case as the technicians processing the scene were liberal with their application of luminol.