West Midlands Police have confirmed that an explosive device left in Birmingham on the night of the 1974 pub bombings has been lost.
Bombs left at two pubs in the city-centre killed 21 people and injured 182.
A third device, left on the same night in Hagley Road, failed to explode.
Only its detonator went off, which meant it mostly stayed intact and was kept by detectives.
Today, Chris Sims, Chief Constable of West Midlands Police, revealed to ITV Central News that it had been lost, despite extensive searches.
He described how it was likely that the device had been disposed of in the mid 1980s.
"By the time the 1991 reinvestigation looked at the exhibits again, 35 of those pieces were no longer there.
"That inquiry tracked back to try and find them and was unsuccessful.
"We have done the same looking in places."
ITV News Central Correspondent Keith Wilkinson has said a "potential treasure trove" of forensic evidence has been lost.
Eric Francis, a former detective inspector who was working for West Midlands Police on the night of the attacks agrees.
He said it was a "sad shame" that the device had been lost.
"We didn't know about DNA then. We didn't know a lot of things then that we know.
"It would have been a marvellous clue."