In my opinion it definitely isn't a cooper.
In my experience, when a tv show centers around a mystery that's supposed to last the entire season, they always try to make you think it's all these other people who killed the person first before revealing who it actually was, and the person who it actually was usually is a surprise. Think Ian or Toby from Pretty Little Liars. We aren't even halfway into the season yet so for them to be Laying all this groundwork this early for Hal or Alice Cooper if they're going to be revealed as the killers all the way at the end of the season seems off. Especially since Alice was always the obvious person because of her comments literally in the first minute of the show. Yeah usually in my opinion the show just tries to distract you with all these false alarms so they can get to the end of the season while giving tons of information but the pertinent stuff not to the end. But I think all the information surrounding Jason is just going to get more and more complicated, and this is just the tip of the iceberg.