It is often said that the accused’s ornamental hammer could not have been the murder weapon because no evidence of blood was found on it. However, possible evidence of blood was indicated on the hammer, but what wasn’t found was Inge’s DNA. And not finding Inge’s DNA does not mean that her blood wasn’t on the hammer.
Regarding the blood: Sgt Peta Davidtsz, forensic scientist at the Biology Unit of the Forensic Science Laboratory, stated that in her opinion and experience the luminol reacted with blood. It is true that there are other substances (e.g. hydrogen peroxide, copper, paint, etc.) that can react with luminol but the colour, intensity and duration of the luminescence when reacting with these substances are different from what would be observed with blood. Blood is also the only substance that show luminescence when a luminol test is repeated.
Regarding Inge’s DNA: There is a saying: Absence of evidence is not evidence of absence.” Given what is forensically known about collecting and testing DNA samples, it should come as no surprise that Inge’s DNA wasn’t found on the hammer. DNA is only found in white-blood cells – not in red-blood cells. Luminol reacts with red blood cells, even at very low concentrations. Less than 0.2% (1 in 500) of blood cells are white blood cells, which contain DNA. It is difficult to detect white blood cells from a weapon that has been thoroughly cleaned. Cleaning removes blood and can seriously damage DNA. It is also likely that the luminol extraction that was used for the DNA testing contained a higher concentration of Mr Fred van der Vyver’s epithelial cells than white blood cells from blood. These epithelial cells could easily have been deposited while handling the hammer immediately before the police took it into evidence. The DNA in these cells could have masked the DNA in Inge’s white blood cells.
We make no conclusive claims, except that the issue of not finding Inge’s DNA on the hammer does not conclusively prove blood was not present on the hammer. It is an established scientific fact that luminol-positive blood samples seldom provide usable DNA profiles.
The hammer page