Toni
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Nonsense. DNA from semen stains have been identified in samples as old as 50 years:
Of the 14 semen stains tested, 12 out of 14 stains (86%) produced strong, positive test results for acid phosphatase (including a semen stain almost 50 years old!).
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Full profiles (10 loci) were obtained from 18 of the 22 samples (82%) (e.g. blood, saliva, semen and vaginal samples) as follows: C-1, C-2, C10, C-11, R-7, R-8, R-9,R-10, S-2, S-3, F-1, F-2, A-2, A-3, Fr-2, Fr-4, Red-1 and Red-2.
b. Partial profiles [types were obtained at most loci] were obtained from 2 of the 22 samples (9%) (e.g. one semen and one bloodstain): (a) Fr-1
[bloodstain made in 1974 and held at room temperature] and (b) Fr-3 [one semen stain made in 1975 and held under a variety of conditions].
c. Only the amelogenin locus, which is the smallest locus of this multiplex, was noted in 2 of the 22 samples (9%): (a) A-1 [semen stain made in 1952 and held at room temperature] and (b) C-3 [bloodstain made in 1975 and held frozen/refrigerated or at room temperature]
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1. Most samples [82%] from this study yielded full profiles. Given the range of ages of these stains and the various storage conditions in which these stains were maintained, it is clear that DNA is a very stable molecule and it is quite possible to obtain a complete DNA profile from samples that are quite old. Full profiles (10 loci) were obtained on samples that were more than 25 years old and which were described as being stored at room temperature.
And here's a study showing: Persistence of DNA from laundered semen stains, where the attempt was to wash out the semen.
And here's one on the persistence of DNA on clothes after exposure to water for different time periods-a study on bathtub, pond, and river (also evidencing the durability of DNA even in cases where clothing has been submerged for months in a river or pond and exposed to nature).
And DNA from burned remains of US soldiers in Viet Nam have been used to identify the remains and return them to the US and their families for burial.