Buddy found a bunch of stock certificates in his house, unsure if he can claim them or not.

Asking on behalf of a friend since he doesnt wanna make a reddit account…

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My buddy was recently renovating his place and came across a small container that was filled with stock certificates, but unfortunately they're not under his name. He believes they belong to the previous owner of the house, which he's unsure whether or not is still alive. Most of the certificates are from the 90's and onwards, and after tallying the amount they're worth almost $100k. Thats a huge life changing amount, but didn't know if he's even able to cash them in since its not under his name. Any advice on this?

Thanks!