The NASA contract engineer who killed a hostage and then himself at the US space agency's highly-secured Johnson Space Centre in Houston, Texas, during a stand-off had received a poor job review and feared that he could be fired, according to police.
Less than a week after the bloodiest campus shooting in US that left 33 people dead, 60-year-old William Phillips took two co-workers hostage at an office building of the space centre on Friday and killed one of them before turning the weapon on himself.
"Phillips was undergoing a job review due to poor job performance," Houston police said on Saturday.
He confronted his superior David Beverly, 62, in latter's office about his performance review, then shot him twice and left. He returned and shot Beverly two more times.
Phillips then duct-taped fellow contract worker Fran Crenshaw, who accidentally stumbled on the scene, to a chair, holding her for hours. Officers freed her after hearing the gunshot that killed Phillips.
Authorities reported that on March 16, Jacobs Engineering Group Inc, of which Phillips was an employee, sent an e-mail to him about his work performance. On March 18, Phillips purchased a .38-calibre revolver and 20 rounds of ammunition.
A copy of the e-mail was found in Phillips' lunch bag on the day of the shootings.
On Friday, Phillips went to have lunch with Beverly and another man. His demeanour was slightly unusual, police Lt Larry Baimbridge said.
About 1:25 p.m. local time, Phillips went into Beverly's office, investigators said.
According to a statement from Crenshaw, who was also in the office, Phillips pulled out his gun and said, "You are the one who's going to get me fired."
After Beverly talked with Phillips for several minutes, Phillips shot him twice. He then returned and shot Beverly twice more, officials said.
Throughout the three-hour ordeal, Phillips watched the events on TV, Crenshaw said. At 4:28 pm, more gunshots were heard, and law enforcement officers entered the office and found both men dead.
"It was obvious" that Phillips went there to kill himself and Beverly, Baimbridge said.
During the standoff, Phillips did not threaten Crenshaw, who was not injured. Although Crenshaw had duct tape on her mouth, she was able to remove it and call security. Crenshaw and her husband are very close friends with the Beverlys, Baimbridge said.
"She was very courageous," Houston Police Chief Harold Hurtt said, adding, "It was a positive relationship between her and the suspect."
NASA is currently reviewing its security measures to find out how the gun was smuggled into the high-security building. Agency spokesman John Ira Petty said NASA was conducting what he called a continuous review of security procedures.
Mike Coats, Director of the Johnson Space Centre, earlier said: "Right now, we are trying to understand why this happened, how this happened. We never believed this could happen here."
Beverly's wife, Linda, said her husband of 41 years was an electrical parts specialist who felt working at NASA was his calling. "David really felt he was a contributor." Her husband had mentioned Phillips before, she added, but declined to say in what regard.
The incident came close on the heels of Monday's shooting rampage at Virginia Tech University in which a South Korean-origin student shot dead 33 people, including two Indians, before killing himself. It again raised the issue of the US gun violence and prompted NASA to review its security measures.
"We will be looking at Friday's events to see if we can improve the security for our employees out here," Coats said in a press conference.
Phillips was provoked by a mid-March job review that criticised him for being late to meetings and other minor offences, said Jacobs Senior Vice President Lon Miller.
Phillips, who worked at the space centre since 1992, bought the revolver from a local gun shop and brought it into work in a duffel bag, officials said.He and Beverly, a quality control engineer with offices nearby in the centre's Building 44, went to lunch with another employee, who said Phillips had acted strangely.