In The Life of Muhammad being A. Guillaume's translation of Sirat Rasul Allah by Ibn Hisham, on page 438 we read:

One of Yamin's family told me that the apostle said to Yamin, 'Have you seen the way your cousin has treated me and what he proposed to do?' Thereupon Yamin gave a man money to kill `Amr b. Jihash and he did kill him, or so they allege.
Supposedly `Amr intended to or suggested to kill Muhammad, but the only evidence for this allegation is that Muhammad had a revelation about this. He is killed not based on facts that he tried to kill Muhammad, but based only on Muhammad's suspicion.

`Amr b. Jihash did not receive a fair trial, somebody send a killer.