There are so many uses of ใจใใ which can all seem quite confusing. My basic understanding here is that ใจใใใฎ has turned the phrase into a noun (similar to how ใฎ can do this on its own) and this is followed by ใ making it a question.
So the whole sentence means something like, Did the criminal swim across this river?
Hereโs a link to a wanikani forum post asking about this grammar point.