Just as "scellé" is used for the bag containing evidence as an extension of the seal placed on the bag (metonymy - that's a word I've been using a lot lately!), so in English we might say "evidence" as an extension of the bag in which the evidence is placed.

Forensic evidence shows that Madril’s DNA\blood was found on Todd’s knife (the murder .... When they opened the evidence in May, the knife was missing. ...
nonprophet.typepad.com/nonprophet/2006/05/guest_blogger_t.html

It is unknown who opened the box, opened the evidence, or mounted the. slides. ...
www.floridasupremecourt.org/clerk/briefs/2003/1201-1400/03-...

Otherwise "evidence bag / box /envelope / packet, etc." as required.

before the state crime lab had even opened the evidence packets in the case. ...
bearingfalsewitness.blogspot.com/2007/04/rush-to-indict.html

bit worse for wear so he opened the evidence bag and selected ONE plant, ...
www.uk420.com/boards/index.php?showtopic=68744

said to have told someone he and a partner opened the evidence envelope and a pic fell out, ... THE FORENSICS CORNER, Crime Cases & Forensic Evidence ...
boards.crimelibrary.com/showthread.php?p=8927873

Do your human forensics lab thing for me. If I'm wrong, I'll look like a dork, ... Jim reluctantly opened the evidence baggie and sniffed cautiously at the ...
angeltowns2.net/sheffield/sentinel/carbon.html