Wiktionary
vb. 1 (context criminology slang English) Conspire to incriminate falsely a presumably innocent person. 2 To furnish with suitable things; to prepare; to fit out.
Usage examples of "fit up".
The guys had declared him insane for even suggesting that it would fit up there.
Doug had shown her how it worked: the little metal thingamajig that held the seven bullets -- the magazine clip, Doug had said -- fit up into the grip, and you had to push the safety hickey with your thumb to engage the firing dololley.
After locking the door I read her the letter I had received, and telling her I could not part from her, implored her to leave home and accompany me on my journey, telling her that on our return to France, I would fit up my chateau in Brittany with all the luxury of an Eastern Harem, where we might reside amid all the pleasures that love could induce, and all the luxury that wealth could purchase.
Next week in Brickhall Magistrates' Court the police will be trying to fit up a fifty-year-old Nigerian woman, accusing her of assault, having previously beaten her senseless.
The port was built after we arrived, and they're too big to fit up there.