HUNTSVILLE, Ala. — A former biology professor accused of killing three colleagues and wounding three others at the University of Alabama in Huntsville has pleaded not guilty by reason of insanity in the shooting.

Standing between her lawyers, Amy Bishop looked down as one of them entered the pleas on her behalf Thursday in Huntsville.

Authorities say Bishop pulled out a gun and opened fire during a February 2010 faculty meeting, killing three professors and wounding three colleagues. Police and people who knew Bishop described her as being angry over the school’s refusal to grant her tenure, a decision that effectively would have ended her employment at UAH.

After the slayings, Bishop also was charged with killing her teenage brother in Massachusetts in a shooting that originally was ruled an accident in 1986.