Well if everyone in the family referred to him as an uncle I think an officer would just put uncle in a simple report and the investigators would later determine the relationship in detail.
I'd bet money that is JM.
From ABC News this morning:
http://abcnews.go.com/GMA/video/missing-girl-isabel-celis-evidence-revealed-16429149
"In one report detectives write about a witness telling them that a guy who was staying with the family owed someone a lot of money, and that was why she was taken."
"One report talks of photograpghs of overall views of the middle-east bedroom, including views of apparent blood on the floor. The room with the apparent blood, according to blueprints, is that is the missing six-year-old's."
The word "apparent" jumped out at me.