A space engineer who killed a co-worker and himself at NASA's Johnson Space Centre acted after receiving a negative job review from his victim.
Houston Police Chief Harold Hurtt said the contract worker, Bill Phillips, initially wounded NASA quality control engineer David Beverly with gunshots and then left the room.
However as Mr Beverly was trying to barricade a door to keep the shooter out, Phillips returned and killed his victim.
Police said that Philips blamed Mr. Beverly for a weak job review.
Earlier today police told how 60-year-old Phillips had worked for NASA for 12 years.
They said Mr Phillips had entered the headquarters of the space agency and taken two people prisoner. He killed one of the hostages before killing himself.
Police who had surrounded the scene entered when they heard a gunshot and found the second hostage alive.
She had been tied up with tape.
The director of Johnson Space Centre in Texas said there would be a review of security at the centre.
NASA also said that it had already reviewed security following the massacre at the Virginia Tech University but would now look again at its arrangements.
