>He was convinced that it was someone from the neighborhood that did the crime.
Yes, moreover I believe he was quite convinced that it was a rather young person from the neighborhood.

Ofcourse, he may be correct. We do not know. It is wrong, however, for a sleuth to be so 'convinced' about anything. Looking at the evidence and being receptive to new evidence and new interpretations is important.

I've always admitted that someone from the immediate area is the easiest person to approach the house without being noticed. I've always felt an 'observation post' such as a nearby home is a likely factor. However, without a neighborhood canvass its a hard avenue to follow and in this particular case it seems unlikely to me that it was a teenage male.