Well, when he is surrendering unarmed with his hands up?
When you have no idea he is a drug dealer?
When he is turning himself in to testify about other crimes?
I presume your comment was hyperbole, and that you are not in fact advocating summary capital punishment for every person dealing drugs, administered without due process by police officers on the street.
Don't forget that those officers are now empowered to determine citizenship status on-the-fly, and if the subject is illegal they get a free Constitutional pass.