When Alexis finds out Jagger was killed she'll assume Kristine 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.
Why would Kristina be arrested? It's Sonny's gun and the last one to touch it was Alexis, who was seen throwing it into the river. She also threatened Jagger the day he was killed. The cops don't know Kristina took the gun from Sonny's place.
Sonny will play "hero" to save Kristina -- ignoring the fact that shooting Jagger in cold blood isn't exactly heroic. But who cares ... it's Sonny and even if he goes to jail they will find a way to have him released after a short stay.
That's everyone. Julian, Sonny, Cyrus, Drew, Johnny etc...as long as they are "main characters" you can't keep them in jail for long unless the writers don't want to use them, like Nikolas currently. So unless MB is leaving, Sonny won't be in prison for too long. I think the last time he was in prison he was in there a couple months tops.
