Really good.
It was pretty easy to me. I didn't figure out right away who the murderer was. But after some time it became a bit simple. Below is a bit of a spoiler so don't look if you haven't beat the game.
Everyone would think it's Charles, but you if you think, you'd get the part that it was a frame. Before you even figure he's innocent. Everyone hated him so you'd then think he must be the one. Most the things that went on in the beginning, led you to think that it was Charles. Which was a pretty good thing to add into the game. When I saw the clown rag on the blade, I then knew right away it was a frame. Before I did anything with it I knew they were framing Charles to be honest. I'm into detective sort of stuff, so yeah. :) And if you saw that in the bosses office the wire cut. And you then found the wire cutter. If you were smart enough, you'd add up the information and go to the Engineer knowing he cut the wire. I won't say much more, because I can bet you someone is reading this that didn't beat the game.
If your smart some of the information/clues adds up before you do anything.
Two more things. You should of hid the items better. Besides that, good game. Great game. You should make more, and have the same detective throughout the mysteries. Like just make new characters and a new mystery. Then when the same detective comes back, you wouldn't need to make more drawings or come up with a new name and junk. I'd definitely hope to see more games of yours like this. If you do think to make another, good luck with it.