We don't know where he is. From what I've gathered, he's ran away from the ship. The one mech who can help us is Astrotrain, and he refuses to speak to me.

[Considering that he jailed his friend Four, he doesn't want to help Security at all.]

If you want to help, find Dreadwing and take him to the brig. He has to spend plenty of time in there. [Not that he expects Grimlock to go through the proper procedure, but he hates being unable to stop all of these murders, and the frustration is growing with Grimlock's accusations.]