Well, the point of capturing the second guy alive was to use him to find out if anyone is involved.
Also, FYI for those not in the USA, everyone is a "suspect" or "alleged" until proven guilty in a court of law. So you could go up to a guy in the center of giants stadium, with 100's of TV cameras and 1000's of fans watching, and mug him, and you would be considered a "suspect" in the robbery until a judge and jury says otherwise.
"Scissors are overpowered. Rock is fine." -Paper