Here's how Jordana Brewster's Dr. Cahill left the Lethal Weapon TV series. Lethal Weapon is a classic of the buddy cop genre and sees Danny Glover's veteran cop Murtaugh partnered with Mel Gibson's live wire Riggs. The chemistry between the two leads combined with Shane Black's witty script and Richard Donner's slick direction propelled it to box-office success. A sequel was quickly put in development, but while Black penned a darker script that ended with Riggs dying, his draft was largely rewritten and Riggs was kept alive for future sequels.
While the first two movies are well-regarded, Lethal Weapon 3 and 4 were mediocre entries. The final movie at least featured a couple of good sequences, especially a brutal final battle between the two cops and Jet Li's villain, but the formula had grown stale. Black once developed a fifth movie that saw Riggs, Murtaugh and the latter's son dealing with a heist during a snowstorm, but it failed to move ahead. Instead, a Lethal Weapon TV series starring Clayne Crawford and Damon Wayans as Riggs and Murtaugh hit screens in 2016.
While there was little anticipation for the new Lethal Weapon prior to its debut, it turned out to be a surprise hit with viewers. Despite this, the show is probably best remembered for its various behind the scenes dramas, with Crawford being fired following season 2 for verbal clashes with Wayans. The show made the gutsy choice to kill off Riggs and replace him with new character Wesley Cole (Seann William Scott). Season 3 also saw the exit of Jordana Brewster's Dr. Cahill, a police psychologist.
During the first two seasons of Lethal Weapon, Cahill grew close to Riggs as they held therapy sessions. She helped him come to terms with the death of his wife and there were hints of romantic tension between the pair too. Riggs and Murtaugh also saved Cahill from a stalker during a season 1 episode. Following Crawford's firing there were reports Jordana Brewster had quit the show in solidarity with her co-star, and while the actress had never confirmed this, Dr. Cahill only appeared in the first two episodes of season 3.
There was no grand exit for the character either, with her final appearance coming in Lethal Weapon season 3 episode "Need To Know." The story revolves around Murtaugh getting used to his new partner and asking Cahill to read up on him and meet him for herself. This ends up with Cole turning down her "romantic" advances in the breakroom, and she quickly breaks off the conversation. Jordana Brewster's final scene as Cahill sees her give a blunt assessment of Cole to Murtaugh, though she thinks his cockiness is probably masking some scars, and she mentions how the loss of Riggs is still affecting her too. While Cahill was presumably still with the LAPD, the character wasn't seen beyond this episode and the show itself was cancelled by the end of the season.