BIRMINGHAM, Ala. — A former biology professor accused of pulling a gun from her purse and opening fire at a faculty meeting pleaded guilty Tuesday to killing three colleagues and wounding three others at the University of Alabama in Huntsville in 2010.

Amy Bishop, 47, pleaded guilty to one count of capital murder involving two or more people and three counts of attempted murder during a hearing in Huntsville. She had earlier pleaded not guilty, and her lawyers said she planned to use an insanity defense.

Prosecutors agreed to recommend a sentence of life without parole for the capital charge, and three life sentences for the attempted murder charges. Sentencing will follow a brief trial on Sept. 24 before Madison County Circuit Judge Alan Mann.

Prosecutors say Bishop opened fire at the meeting on Feb. 12, 2010. Her attorneys say Bishop had mental problems; she signed a plea agreement with a barely legible scrawl.

Bishop, who lived with her family in Huntsville before the shootings, also is charged with killing her brother in Massachusetts in 1986. The shooting of 18-year-old Seth Bishop had been ruled an accident after Amy Bishop told police she shot him in the family’s Braintree home as she was trying to unload her father’s gun.

But the Alabama slayings led to a new investigation and charges.

In the school shooting, police and people who knew Bishop have described the Harvard University-educated researcher as being angry over the University of Alabama’s refusal to grant her tenure, a decision that effectively would have ended her employment in the biology department.

The gunfire killed Bishop’s boss, biology department chairman Gopi Padila, plus professors Maria Ragland Davis and Adriel Johnson. Professors Joseph Leahy, staff aide Stephanie Monticciolo and assistant professor Luis Cruz-Vera were shot and wounded.

Debra Moriarity, who was in the faculty meeting at the time of the shooting and is now biology chairman at the school, said she was OK with the death penalty being off the table and relieved that the case is nearly over.