After lunch Friday, police say, he walked into David Beverly's office, a .38-caliber gun in hand, and said, "You're the one who's going to get me fired!"
Beverly tried to calm him — then shots rang out.
Hours later, authorities stormed the space center and found Phillips had shot himself while holed up with a hostage. Beverly also was dead, and police said Saturday the apparent murder-suicide may have occurred because Phillips feared being fired.
The hostage, Fran Crenshaw, a contract worker with MRI Technologies, was freed.
Police Chief Harold Hurtt said Phillips bought the .38-caliber revolver and 20 rounds of ammunition March 18, two days after receiving the e-mail that cited deficiencies in his work and an improvement plan he was to follow. A copy of the e-mail was found in Phillips' lunch bag on the day of the shootings, police Lt. Larry Baimbridge said.
Beverly, a 62-year-old electrical parts specialist, tried to talk to Phillips for several minutes to calm him and suggest ways he could improve his job performance, police said. Authorities praised him for his bravery while trying to protect Crenshaw, who worked in his office.
"Heroes just don't fly in space," Hurtt said. "Sometimes heroes work in the next cubicle next to you."
Phillips, an employee of Jacobs Engineering of Pasadena, Calif., had worked for NASA for 15 years. He was unmarried, had no children and apparently lived alone.
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 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.
Space agency spokesman John Ira Petty said Saturday that NASA was conducting what he called a continuous review of security procedures. Petty would not discuss specifics, saying the apparent murder-suicide was a police matter.
To enter the space center, workers must show an ID badge as they drive past a security guard. The badge allows workers access to designated buildings.
NASA Administrator Michael Griffin said "there are always lessons to be learned" from events such as the shootings, but that there is no way to absolutely guarantee safety.
"This individual came in ... determined that at the end of it, he was going to die, and before he did, he wanted to satisfy a grudge," Griffin said. "It is essentially impossible to stop such a person."