Factual error: In the closing credits, Eva Mendes' name is spelled as both Eva Mendes and Eva Mendez.
Character mistake: At end when Jake has the 1911 single action automatic covering Alonzo, it is not cocked. Since the 1911 is single action, he can't fire it until he cocks it which he does just before he shoots him in the butt. Makes no sense not to have it cocked the whole time he has it trained on Alonzo.
Continuity mistake: The first time Ethan apprehends the green car for possession, the person in the passenger seat is a woman in all exterior shots. From the interior it's always a man.
Continuity mistake: When the crew are raiding Roger's house, they approach the door and the handle is on the left. One guy kicks open the door - from inside the house the door swings open the opposite way. (01:03:30)
Continuity mistake: After Ethan and Denzel get away from the shoot-out near Sandman's house, they pull onto the side of the highway, under an overpass. The close up shots of the actors show sunlight on their faces. Wide shots of them have them in the shadow of the overpass.
Continuity mistake: In the bar scene, Stan has a long stray hair on his left eyebrow. The backdrop is the window and it's easily visible. A few moments later the stray hair is gone.
Continuity mistake: When Alonzo shoots his partner in the vest twice, he injures him on his right side. In the next screen, he is on a stretcher holding his left side.
Answer: They grew sick and tired of Alonzo's arrogance and probably decided he wasn't worth the effort. Alonzo was however killed by the Russian Mafia because Jake was told that Alonzo killed one of their couriers and had to pay them one million dollars by midnight or he would be killed himself.