PHILADELPHIA (AP) — A woman who was convicted of fatally shooting two co-workers at the Kraft Foods plant in Northeast Philadelphia was formally sentenced to life in prison.

Earlier this month, a judge found Yvonne Hiller guilty of two counts of first-degree murder and other counts in the deaths of 47-year-old Tanya Wilson and 36-year-old LaTonya Brown.

First-degree murder carries a mandatory sentence of life in prison without parole, so Monday’s sentencing is a formality.

Hiller had been suspended the evening of Sept. 9, 2010, the night of the shootings, after making violent, profanity-laced threats against co-workers. But she returned from her car minutes later with a loaded .357 Magnum.

Defense attorneys had argued that Hiller was motivated by a deeply held belief that her co-workers were poisoning her.

(Copyright 2012 The Associated Press.)