With regard to the shooting at Brown University in Rhode Island, several have raised questions about how they could arrest someone as a “person of interest” and then release him. They detained a youngish man who had driven there from Wisconsin and had two handguns in his hotel room.
My guess is ballistics showed the bullets fired on campus didn’t come from his weapons. Or a trace of his cell phone whereabouts showed he wasn’t on campus during the shooting. Or even checking his alibi found he had a lawful reason to travel to RI. Any of those could signal “cut him loose.”
Detectives claim not to believe in coincidences, but if pressed will admit they occur.