The objection is structurally compelling. The blood sample used in 1996 came from clothing that had been held in a museum for over 160 years. Museum environments are not sterile, and the individuals who have handled, cleaned, and preserved those items over the decades have contributed their own DNA to the surface of the artifacts. If the bloodstain on the underwear was contaminated with modern blood — from a museum worker, for instance — then the DNA result would reflect that contamination rather than Hauser himself.
For the hair samples, the authentication challenge is different but real. The locks of hair used in the 2024 study came from private collections with documented provenance histories, but provenance documentation is not the same as scientific verification of the sample’s origin. Someone could, in principle, have substituted hair from a different person at any point in the chain of custody. This is not an accusation; it is a logical possibility that any rigorous analysis must address.
The Parson team addressed this problem through multiple strategies. First, by analyzing hair from three separate locks with different provenance histories, they could check for consistency: if all three locks produced the same mitotype, that consistency strongly suggested the samples were genuine, because the probability of three different improperly substituted samples all producing the same result by chance is very low. The results were consistent.
Second, by using the PEC MPS method, which differentiates between very short, highly fragmented ancient DNA and longer, intact modern DNA, the researchers could distinguish the signal from authentic near-two-century-old hair from any modern contamination. The ancient DNA they recovered showed the fragmentation pattern expected from material of that age.