A 60-year-old Nasa contract worker took a handgun inside an office building at the Johnson Space Centre and shot dead a hostage before killing himself.
A second hostage, Fran Crenshaw, who had been tied to a chair with duct tape, escaped from the centre in Houston, Texas, with minor injuries, police Capt Dwayne Ready said.
The gunman, William Phillips, was able to take a revolver past Nasa security last night and barricade himself in the building, which houses communications and tracking systems for the space shuttle.
Phillips had apparently had a dispute with murdered hostage David Beverly, a civil servant who worked at the agency.
Beverly, who was shot in the chest, was probably killed “in the early minutes of the whole ordeal”, police said.
Today, Nasa spokesman Doug Peterson said the agency would review its security.
“Any organisation would take a good, hard look at the kind of review process we have with people,” he said.
To enter the space centre, workers flash an ID badge as they drive past a security guard. The badge allows workers access to designated buildings.
Phillips, an employee of Jacobs Engineering of Pasadena, California, shot himself once in the head more than three hours after the stand-off began, police said. Initial reports indicated two shots were fired at about 1.40pm local time and another shot was heard about 5pm.
John Prosser, executive vice president of Jacobs Engineering, confirmed that the gunman was a company employee but would not release any information about him.
Police said investigators searched the gunman’s house where he lived alone, and found no guns or any evidence about the shooting.
Mike Coats, the director of the Johnson Space Centre, said Phillips had worked for Nasa for 12 to 13 years and “up until recently, he has been a good employee”.
Police Chief Harold Hurtt said there was apparently a dispute between Phillips and Beverly, but did not elaborate.
During the confrontation, Nasa employees in the building were evacuated and others were ordered to remain in their offices for several hours. Roads within the 1,600-acre space centre campus were also blocked off, and a nearby middle school kept its teachers and students inside as classes ended.
Doors to Mission Control were locked as standard procedure.
Nasa employees and contract workers were kept informed of the situation by email.
Michael Zolensky, who studies cosmic dust, said workers were gathered around a television watching news reports of the situation.
US president George Bush was informed about the gunman as he flew back to Washington from an event in Michigan, White House spokeswoman Dana Perino said.
Jacobs Engineering provides engineering for the international space station, space shuttle and other spacecraft programmes and conducts research and development for new technology.
Beverly's wife, Linda, said today her husband was an electrical parts specialist and had recently celebrated 25 years of service with Nasa.
She said her husband had mentioned Phillips to her before, but refused say in what regard, saying it would not be fair to Phillips.