The gunman who killed a hostage and himself in a stand-off at a Nasa centre in Texas blamed his victim for a poor work performance review, police said.
Police evacuated staff and cordoned off roads
William Phillips, 60, took a revolver to work at the Johnson Space Center on Friday and shot dead fellow employee David Beverly, 62.
Phillips bought the gun on the same day last month that he printed off the bad review, police said.
A woman was also held hostage in a four hour ordeal but was only slightly hurt.
Nasa said Phillips, a contract engineer, had been employed for about 12 years, was unmarried, had no children and reportedly lived on his own.
Nasa officials said Phillips brought the revolver into a building that houses communication systems for the space shuttle.
Phillips confronted Beverly, a quality-control engineer, about the review and despite attempts by his victim to calm him, shot him twice.
The stand-off took place in the communications Building 44
Phillips left the room briefly but later returned and shot Beverly another two times as he tried to resist, police said.
"The suspect blamed Mr Beverly for being responsible for his negative job-performance situation," Houston Police Chief Harold Hurtt said.
Nasa said the woman hostage, Fran Crenshaw, was tied to a chair for hours and succeeded in providing a calming influence, preventing the situation from getting worse.
Phillips held her hostage until he shot himself dead.
Nasa says it is undertaking a review of security procedures.
It evacuated some employees in the building when the situation occurred while others were ordered to stay in their offices.
The Johnson Space Center contains Nasa's mission control, which oversees the agency's space flights.
Doors to mission control were locked and outlying roads cordoned off.
The stand-off came less than a week after a gunman killed 32 students and teaching staff at Virginia Tech university before killing himself.
There has been a rash of security alerts across the US, which is also marking the eighth anniversary of the Columbine school massacre in which 15 people died.