If this was a Castle episode, my money would be on a former male CG member.
Someone who was out of shape, came to camp and got in shape, was shown attention by the deceased because she is a passionate leader who cared about her team's health, his advances were rejected, he quits and goes back to being out of shape, finally snaps when their paths cross, and he plots her end.
Him snooping around the church might have been looking for a place to hide or making sure no one else was there.
Someone who was out of shape, came to camp and got in shape, was shown attention by the deceased because she is a passionate leader who cared about her team's health, his advances were rejected, he quits and goes back to being out of shape, finally snaps when their paths cross, and he plots her end.
Him snooping around the church might have been looking for a place to hide or making sure no one else was there.