A Co-op City janitor who claimed that losing his job made him crazy was found guilty yesterday of fatally shooting the boss who fired him at the sprawling Bronx housing complex.

Paulino Valenzuela, 48, faces 25 years to life in prison when he is sentenced in Bronx Criminal Court on May 5 for killing Audley Bent, 59, and wounding three other people in the 2007 attack.

Valenzuela, who lived in the complex, went on a rampage after being axed following a series of on-the-job indiscretions — including showing up drunk and bullying co-workers.