At the start of the first Dragon Age, what reason does the player have to add Sven to their party?

All we are presented is that he is a large gray dude who murdered a entire family and the children as well. You are given the option to let him go, but the game never presents any reason to besides "He might be helpful"

There is no reason to believe that this dude wont slit your throat while you are sleeping, it completely baffles me the way they introduced this guy.