4
I propose the culprit is
We know the victim, Johnny, had just enough time to write a short note prior to his death.
He did not seem to have time to come up with something too complex as his body was losing blood quickly, but needed to pass along the victim's name in a manner not completely obvious in case the culprit found it and realized what it was.
So, ...
Only top voted, non community-wiki answers of a minimum length are eligible