[user104658]

Originally Posted by Niamh.

Benji was kind of planned but I still think Joe would have let him go if he was sure he wouldn't get caught out

I think he was fairly content with the video evidence of the drowning being enough to keep him safe, but he got the idea in his head that (ironically) Beck wasn't "safe" with Benji around, though probably the real motivation was that he didn't think Beck would move on if Benji was still kicking around, even if he broke contact with her.