The answer is really clear. It is not his property. It is the property of someone else.
At this point it is not the property of the person that owes him the money. It is the property of everyone else that is left being owed money in the situation.
He has no right to steal that property.
Make whatever excuse you want to justify stealing but it is theft all the same. Don’t be a thief is always a good way to live.
Is his honesty worth nothing more than the value of a used laptop computer?
If you’d read what I said carefully you’d see I said to try and return it.
But you can’t return an item if nobody is there to take it.
Send an Email, ask, find out who to return it to. I am assuming that if the company is closed the door is locked but Email may still be answered. If you do return to make sure to get a signed receipt.
If you make a good effort then there is nothing more to do.