A safe which was flung in the Thames at Greenhithe before washing up in Gravesend is thought to have been stolen.
It was recovered on July 27 at Denton Wharf appearing as though it had been damaged.
At 8.09am that day officers received a report two men had been witnessed throwing a safe over the seawall into the river at Sara Crescent.
Inside was a set of digital scales and other objects too sodden to be identified.
A 22-year-old man from Sittingbourne was arrested the same day on suspicion of theft and bailed pending further investigation until August 27.
Investigating officer, DC Bill Looker, said: "We have reason to believe this safe was stolen before it was dumped but are looking for information to help us establish the circumstances around the theft and to try to help us locate its owner.
"I'd ask anybody with information to call me on 01474 366042.
"Alternatively, to remain anonymous, call Kent Crimestoppers on 0800 555111."