There is no chain of custody involving that gun that's admissible in court. No way to prove it was recently taken from the river. Since it was in the water, Alexis' fingerprints would be gone, right? I could argue that Sonny just took another one of guns, dipped it in the water and mailed it to the cops. It's not like Liz or Ric had a deep, personal relationship with this weapon and can pick it out of a line up. "Yes, officer! That is the gun I saw for all of 2 seconds being tossed off a bridge in the dark of night. I'd know it anywhere!". Any good DA could get this so-called evidence tossed.
Also, I hate Kristina. What a horrible, stupid, annoying character. Why can't she die soon instead?
On a bright note, I did enjoy Lucas and Ava scenes today. I'd forgotten they both played respective members of the Snyder family on ATWT. And looks like Brad is on to Portia. Go with God, my sneaky son.