[Jordan.]

Originally Posted by ukturtle

Firstly, we don't actually know that the letters are representig their names and secondly, one of those letters could be fake. There is at least one hoax clue from those we have already got.

My guess is that 'M is fake. That would leave it to those who have N and S in their name. That makes 4 suspects?

Oh that makes sense!

So the killer MUST have already been in isolation once and brought back a false clue meaning the people who haven't yet been in isolation are innocent.