I can’t fully answer this, but you could put something like...
Dear Sheriff,
____ committed the crime. I got this information from ____ the type of source is ____ from ____. The purpose is ____ and this was a ____ source. This source is the most reliable, because ____.
The source that was least reliable was ____, because____. The type of source is ____ from ____. The purpose is ____ and this was a ____ source. This source is the least reliable, because ____.
Sincerely,
Detective
I’m sorry that this isn’t actually answering the blanks I left, but I haven’t actually ever answered this question:(
I just want to try to help, so here is a format!