Rez spotted some motion out of the corner of his eye, and creeping carefully along for one as big as himself, he was able to spot them entering one of the buildings without them noticing him tailing them. He couldn't count on the other rabble to do his job for him, at least not completely. He'd certainly "help" them out a bit because he had little choice in the matter. They'd be joining the fight momentarily if he wanted them too or not, so might as well make the most of them. 

He situated himself behind a corner overlooking the street with a great view of the building they were situated inside. The other group would be attacking from the other direction so Rez was effectively in their backfield. Should they make a mistake during the gunfight he would get in on the action to pick them off one by one.