Harvard-educated biology professor Amy Bishop, accused of murdering three colleagues at the University of Alabama in Huntsville, pleaded not-guilty by reason of mental disease or defect on Thursday.

Bishop allegedly shot six people, killing three, at a faculty meeting in February 2010 after the university refused to grant her tenure. She faces charges of capital and attempted murder, and the prosecution is seeking the death penalty.

After entering her plea, Bishop was taken back to the Madison County Jail, where she will stay until her court date on March 19.

Bishop had also been indicted in the killing of her brother in 1984. Bishop, then 19 years old, shot her brother three times before attempting to escape in a stolen car.

After her involvement in the February shooting, authorities reopened the case of her brother’s death.

Bishop had originally told the police that she accidentally shot him, a claim upheld in the original investigation. The more recent investigation revealed no new information.

In 1993, police also linked Bishop to the attempted bombing of a Harvard medical professor. Although never charged, Bishop and her husband were questioned by authorities investigating the delivery of a package containing two unexploded pipe bombs to Paul A. Rosenberg, an associate professor of neurology at Harvard Medical School.

Bishop received a PhD from Harvard that year.

Despite her ties to past criminal investigations, Robert L. Broussard, district attorney for Madison County, Alabama, said evidence from those investigations will not be submitted in the trial. But Bishop’s prior crimes may surface in discussions about her emotional and mental competency at the time of the shooting.

Now, Bishop faces the “burden of proving that she was insane at the time”, Broussard said.

Because the judge has imposed a gag-order on case details, Broussard declined to comment on the prosecution’s strategy moving forward with the case. Roy W. Miller, Bishop’s attorney, was not available to comment.

This article has been revised to reflect the following correction.

CORRECTION: SEPTEMBER 25, 2011

The Sept. 23 story "Harvard Ph.D. Amy Bishop Appears in Court for Allegedly Murdering Colleagues" incorrectly identified the original investigation into the death of Bishop's brother as a trial. The case was ruled an accident.