How do i decrypt/read whatsapp backup file? (.db format)

I found a microSD card in a bad area here, lots of junkies, heroin addicts, thieves, etc, i inserted it into my computer to find out what's on it, turns out it was some not-so-fortunate guy's phone, he had photos of his family and kids there, and i want to find him and return him the memory card, probably his phone was stolen and whoever did it threw away the card.
I found no leads about him so far, only 3 whatsapp backups that i can't seem to be able to decrypt anyhow (I need to, maybe i can find his wife's number and contact her).

I'd appreciate any help, i really would like to return it, he probably would be happy.. afterall... these are memories..