yeah... if the police found a speck of blood of sperm, they
would be able to obtain the DNA from it. This DNA would then be
used to search on a DNA database, which contain the DNA profiles of
criminals caught in Singapore. (Non criminals would not have their
record in this database). If no match is found, then this record is
kept and case is unsolved.
Only if a person is suspected, then he or she will be asked to
do a blood test and the DNA profile would then be matched against
that of the profile gotten from the blood/sperm.
There was this case whereby this guy raped a girl and after
which clean off the area for any fingerprints of himself. He
thought he got away scot free, but he still got arrested 15 years
later when his nephew was caught the police. The police traced the
nephews DNA profile to that of the sperm's DNA profile gotten from
the crime scene and realised that it kind of matches the profile
(though not identical). So each and every family member of the
nephew was brought in to do a DNA profile, and the rapist was thus
caught.
There are many ways on can disrupt the DNA at the crime scene
using chemicals. And what the forensic drama from HK showed is
indeed true to what our professionals in Singapore are doing.
Hope this helps.
