When Alexis finds out Jagger was killed she'll assume Kristina did it. Then Rick will tell the police he saw Alexis throwing something (not a phone) into the river. The police will find the gun in the river and since we were told Kristina got the gun from Sonny it will match the type of gun that Jagger was shot with. So Kristina will be arrested.
Or maybe it'll turn into a "Who Shot Jagger?" storyline. Everyone without an alibi and motive: Kristina, Alexis, lucky for Ava, apparently she's now off the hook.
Kim