All it says is, he's a person of interest. He may not have subdued and killed anyone. But the police have no way of finding out who the real perps were, if he wasn't the sole actor, or involved in the killings at all. How do you track down Mexican cartel members? Those dudes would be long gone. They know how to cover their tracks. (Speaking speculatively). So Kennedy's the fall guy, and maybe he knew that, which could be why he ran to Florida.
How could they prove he did it, anyway? Maybe they just want to question him further (they already did once, before he disappeared). IMO they don't know anything for sure, unless they have some evidence they're not talking about.
I think it's still a mystery.