> a limp handshake relays less DNA than a bone-crushing one
Bowing seems to make good sense in this context.
Finally, shocking he wasn't compensated for spending a long time in jail.
Remember: DNA "matches" are probabilistic, and most of their utility has been based on the low probability of a sample taken from a crime scene "matching" a sample taken from a suspect. Prosecutors (committing the prosecutor's fallacy, of course) love to tout the "one in a billion" type statistics for a match being a false positive, but it doesn't take a very large database at all for "one in a billion" coincidences to start occurring.
DNA evidence is like a magic bullet for crime, DNA found -> guilty is the norm, not the exception.
As far as the statistics are concerned: we do not actually know the false positive rate.
Nevertheless, it is likely that a traditional investigation would have found them out too. Especially through the link between the victim and the sister, coroborated by phone records. Finally, their culpability could have been put beyond doubt by using a DNA test.
This is a broad-based problem.