No matter what. Regardless of weather or not he dropped the welder off he is still responsible.
If I borrowed your vehicle, than brought it back gassed up and than some DB stole it from your drive way. Who would be responsible? Me or the DB? All you have is my word that i dropped it off, nothing more.
So unless you have known me since childhood you would have no reason what so ever to believe me.
Bad example yes but im just sayin. the kid that borrowed the welder is fully responsible.