An investigation into a mail bomb sent in 1993 to a Harvard professor has been closed, Massachusetts' top federal prosecutor said Thursday, following a review of the case prompted earlier this year by the arrest of former professor Amy Bishop.
Bishop faces capital murder and attempted murder charges in the shooting of six colleagues, three of whom died, during a staff meeting at the University of AlabamaÂ in Huntsville on February 12.
Her arrest prompted several law enforcement agencies and media outlets to take a closer look at her past brushes with the law,Â among them herÂ suspected involvement in the attempted mail bombing of a Harvard Medical School professor in 1993, according to The Boston Globe.
At the time, Bishop was working as a postdoctoral fellow in the hospital's human biochemistry lab. She and her husband, Jim Anderson, were questioned after a package containing two pipe bombs was sent to the Newton, Massachusetts, home of Dr. Paul Rosenberg, the Globe said, citing a law enforcement official.
The U.S. Attorney's Office in Massachusetts undertook "an appropriate and thorough investigation," to determine the source of the incendiary device, U.S. Attorney Carmen Ortiz said inÂ a statement Thursday.
Despite those efforts there was insufficient evidence to bring charges, Ortiz said. The matter has been closed and the office does not intend to reopen it.
This year's shootings also prompted a Massachusetts judge to open an inquest into the 1986 shooting death ofÂ Bishop's brother, Seth, which was ruled an accident. The inquest resulted in a grand jury indictment in June against Bishop on a first-degree murder charge.