There's a murder trial ongoing in Ireland at the moment and one of the pieces of evidence is a spade found at the scene along with the skeletal remains. It was contended by the prosecution that this spade was belonging to the defendant but while they were similar
"forensic evidence found the paint splatters on the spade were not the same as on the [defendant's] garden fence"
My question is: can something left out in the open be changed either chemically or structurally by the environment such that it appears to be similar but not the same? If so why would this not have been called out as a caveat by the expert forensics witness?
The specifics of the chemical tests weren't gone into in the media (sample article here) so I don't know how accurate it was.