HOUSTON (AP) – NASA officials who examined their security measures following the deadly shooting at Virginia Tech are trying to figure out how a contract worker sneaked a handgun into the Johnson Space Center and killed another employee before shooting himself.

The gunman, armed with a snub-nosed revolver, barricaded himself in a building that houses communications and tracking systems for the space shuttle. He shot and killed a man and duct-taped a woman to a chair for hours before finally shooting and killing himself, police said. The woman hostage suffered minor injuries.

“Right now we’re trying to understand why this happened, how this happened,” Mike Coats, director of the Johnson Space Center, said in a news conference. He said they had reviewed their procedures earlier this week because of the Virginia Tech shootings.

“But of course we never believed this could happen here to our family and our situation.”

NASA spokesman Doug Peterson said the agency would review its security.

To enter the space center, workers flash an ID badge as they drive past a security guard. The badge allows workers access to designated buildings.

NASA and police identified the gunman as 60-year-old William Phillips. He apparently had a dispute with the slain man, Police Chief Harold Hurtt said without elaborating.

NASA identified the slain man as David Beverly, a 62-year-old NASA worker. Beverly was shot in the chest and was probably killed “in the early minutes of the whole ordeal,” police said.

Beverly’s wife, Linda, said her husband of 41 years was an electrical parts specialist who felt working at NASA was his calling.

“His intellect and his knowledge, David really felt he was contributor,” she said.

Her husband had mentioned Phillips before, but she declined to say in what regard. Linda Beverly said it wouldn’t be fair to Phillips.

The second hostage, identified by NASA as Fran Crenshaw, a contract worker with MRI Technologies, escaped after being bound to a chair with duct tape. She who worked in the same general area and was presumably taken hostage after Beverly was shot, Hurtt said.

“She was very courageous, a calming influence in this whole issue and apparently was a very positive relationship between her and the suspect because he at no time that we know of threatened to do injury to her,” Hurtt said.

Phillips, an employee of Jacobs Engineering of Pasadena, Calif., had worked for NASA for 12 to 13 years and “up until recently, he has been a good employee,” Mr. Coats said.

He was unmarried, had no children and apparently lived alone.

The shooter left telephone numbers and names of people to contact and wrote a note on a dry erase board in the room, police said.

“I don’t recall what was on it,” Hurtt said.

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 center 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.

President Bush was informed about the gunman as he flew back to Washington from an event in Michigan, White House spokeswoman Dana Perino said.

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Associated Press writers Rasha Madkour and Mike Graczyk in Houston; Anabelle Garay in Dallas; Jennifer Loven in Washington, D.C.; Mike Schneider in Orlando, Fla.; and Christina Almeida in Pasadena, Calif., contributed to this report