A biology professor at a southern US university was charged with murder over the shooting deaths of three fellow biology professors at the campus.
Authorities said Amy Bishop, an instructor and researcher at the University of Alabama's Huntsville campus, opened fire during an afternoon faculty meeting, killing the three and injuring three other school employees.
Bishop was charged with one count of capital murder, which means she could face the death penalty if convicted.
Bishop was taken in handcuffs from a police precinct to the county jail and could be heard saying, "It didn't happen. There's no way .... they are still alive."
Police said they were also interviewing a man as "a person of interest".
University spokesman Ray Garner said the three killed were Gopi K. Podila, the chairman of the Department of Biological Sciences, and two other faculty members, Maria Ragland Davis and Adriel Johnson.
Two others are in critical condition, and a third who was wounded was upgraded to fair condition.
The injured were identified as department members Luis Cruz-Vera, who was listed in fair condition and Joseph Leahy, in critical condition in intensive care, and staffer Stephanie Monticello, also in critical condition in intensive care.
No students were harmed in the shooting.
Sammie Lee Davis said his wife, Maria Ragland Davis, was a researcher who had tenure at the university.
In a brief phone interview, he said he was told his wife was at a meeting to discuss the tenure status of another faculty member who got angry and started shooting.
He said his wife had mentioned the shooter before, describing the woman as "not being able to deal with reality" and "not as good as she thought she was".
Bishop, a neurobiologist from Harvard University, joined the UAH biology faculty as an assistant professor in fall 2003.
Bishop and her husband placed third in a statewide university business plan competition in July 2007, presenting a portable cell incubator they had invented. They won 25,000 US dollars to help start a company to market the device.
Amanda Tucker, a junior nursing major, was taught by Amy Bishop in anatomy about a year ago.
Ms Tucker said a group of students went to a dean complaining about Bishop's performance in the classroom, and Ms Tucker signed a petition complaining about Bishop.
"When it came down to tests, and people asked her what was the best way to study, she'd just tell you, 'Read the book.' When the test came, there were just ridiculous questions. No one even knew what she was asking'," said Ms Tucker.
Andrea Bennett, a student majoring in nursing, was in one of Bishop's classes on the day of the shootings.
Ms Bennett said nothing seemed unusual, but she described Bishop as being "very weird" and "a really big nerd".
"She's well-known on campus, but I wouldn't say she's a good teacher. I've heard a lot of complaints," Ms Bennett said. "She's a genius, but she really just can't explain things."
Ms Bennett, an athlete at UAH, said her coach told her team Bishop had been denied tenure and that may have led to the shooting.
"She went to Harvard, so she is very smart. I can see that her getting denied tenure at UAH would be pretty upsetting," said Ms Bennett.
Student Erin Johnson told The Huntsville Times a biology faculty meeting was under way when she heard screams coming from a conference room.
University police secured the building and students were cleared from it. There was still a heavy police presence on campus, with police tape cordoning off the main entrance to the university.
The Huntsville campus has about 7,500 students in northern Alabama, not far from the Tennessee line. The university is known for its scientific and engineering programmes and often works closely with Nasa.
The space agency has a research centre on the school's campus, where many scientists and engineers from Nasa's Marshall Space Flight Centre perform Earth and space science research and development.