When forensic materials are handled in court, it is the usual practice for the handlers-- defense or prosecution, lawyers or expert witnesses-- to don a rubber glove first. It is more to protect the health of the handler (in this bloodborne-illness day and age) than to protect the evidence from contamination. Once the evidence is out of the sealed evidence bag, it is, theoretically, deemed contaminated and thus is considered beyond the original chain of custody which brings it to the court sealed, initialled, and provenance documented.
I wanted to tell Johnny Cochran-- "If it doesn't fit, he's faking it."