Thread: Why was Marcus Fenix in jail?

In the beginning of Gears of War, Marcus Fenix is in Jail. Through Gears 1 and 2 it never explains why.

does anyone know why Marcus Fenix was in jail?

This is what I found:

Fenix is the protagonist of the series. He is first introduced as an inmate, serving a prison sentence for abandoning his military post in order to make a vain attempt to save his father, Adam Fenix. Prior to the Locust Invasion, Fenix is noted for having a famed military career, during which he played a notable part in the Pendulum Wars. Despite this, Fenix is left for dead in a dilapidated penitentiary, until Dominic "Dom" Santiago, his friend and former comrade, saves him in the first act of Gears of War. Fenix is shortly reinstated into the military, and assigned to serve with Delta Squad. He becomes the leader of Delta Squad when Kim is killed by RAAM. Fenix leads his comrades across the ruins of Sera, in an attempt to activate to the Coalition's latest weapon against the Locust. When Delta Squad is split up, he teams with Dom.

And the Marcus Fenix biography:

Marcus Fenix is a character from the Gears of War videogame series.
Sergeant Marcus Fenix is a member (and later the leader) of Delta Squad, a four-man team of soldiers fighting for the Coalition of Ordered Governments. He and his fellow “Gears” are part of humanity’s last stand against the encroaching Locust Horde, which threatens to completely wipe mankind off the surface of the planet Sera.

Earlier in his life, Marcus looked forward to a promising career as a military officer. Emergence Day, however, and the chaos that followed, took his life in a very different direction. During a Locust assault on the stronghold of Jacinto Plateau, Marcus took the risk of leaving his defensive position to try and rescue his father, Adam, before his home near East Barricade Academy was destroyed. He was too late, however – Adam Fenix was killed, his family home was razed by the Locust, and the worst was yet to come.

Marcus was tried for dereliction of duty, convicted, and packed off to a 40-year sentence in the Jacinto military prison. Some observers (like his partner Dominic Santiago) felt his trial was merely for show, and Marcus was railroaded without regard for extenuating circumstances, but in any case, he never expected to see the light of day again. Several years later, however, after the Horde overran the prison and COG military commander Victor Hoffman pardoned all its inmates, Santiago managed to get Marcus out of jail and back into the army.

Sergeant Fenix has the bitter, fatalistic attitude of a man who’s known war his entire life, and he’s not exactly on the best of terms with his superiors in the COG hierarchy. Nevertheless, there’s not an ounce of quit in him, and he’s a more than capable leader for his teammates in Delta Squad.