Uh, yes ... Meredith’s bra fastener
A Police videotape (taken on 3 November 2007) showed Meredith's bra fastener, next to where her body was found. At that time, investigators decided it was not important evidence, and did not bag it up.
On 18 December when police returned to the crime scene, they decided that the bra fastener (previously seen as “unimportant”) was very important.
Only then was it subjected to DNA testing. This revealed “microscopic” traces (the words accepted by the Police report) of DNA belonging to Raffaele Sollecito.
This DNA test result is central to the prosecution's case.
But how reliable is this evidence? If you have ever been present in a room and touched something, you leave a DNA trace. Raffaele had been on the premises several times, and would have left his DNA all over the place. The bra fastener had been (literally) kicking around the premises for 6 weeks before it was tested. It’s no wonder Rafaele’s DNA had got on to it.
As for Amanda’s DNA ... of course it had got on to it ... she lived there!
In reality, all that it proves is that, while the bra fastener was kicking around for 6 weeks on the floor, it had become contaminated with DNA from everyone who had recently been in the premises.
2 investigators even admitted having handled it before dropping it into the bag. These 2 investigators admitted that they had also handled items belonging to Amanda. So, the investigators had contaminated the evidence before it got anywhere near the lab.
Conclusion ... the Bra fastener DNA evidence is unreliable and inconclusive ... the view held by the Police themselves, until they suddenly had to save the embarrassed face of a Prosecutor who had already been charged with Abuse Of Authority for trying to trump up evidence on other cases.