Ok, so there are two suicide notes found in the trash in the beginning. Both with complete different handwriting. I'm not sure why this didn't register with our trio, maybe because you just assume, oh maybe it was suicide and not think twice. The note on the left has handwriting that matches not only the threatening notes left on Oliver and Jan's door, but also the meet up note Mabel finds in Tim's book cut out with the jewels. So likely murderer 1, the poison or shooter, is tied in with the jewelry operation. Suicide note 2 actual matches up with the note Jan slide under Charles door asking him out to dinner. Especially the weird way she writes Js. So Jan is likely tied to being the the remaining killer, either the posioner or shooter.