Shaker didn’t have to return Sean

The reward was for the capture or kill of the kidnappers. When shaker put his plan into action Tom and Kate believed Sean to be dead so they wouldn’t be expecting him back, all shaker had to do was take Maris’s gun, go shoot Sean and then put it back in her hand, it just seems like the kind of thing that a scumbag like shaker would do. Plus he could still collect the reward money