SAN DIEGO -- Robert Mack has been a model prisoner at Donovan Correctional Facility.

He has taken almost every self-help course offered and has never violated any facility rules.

However, the shadow of a January day in 1992 remains a part of Mack.

Fired after 23 years at General Dynamics, Mack killed a labor board hearing officer, Michael Konz, and gravely wounded his supervisor, Jim English, who died years later of complications from his injuries.

Mack pleaded guilty to second-degree murder and attempted murder.

"Even though Mack's bullets didn't kill Jim instantly, it drastically changed the quality of his life. It robbed him of his independence, and, ultimately, the bullet fragments in his brain caused the cancer that ended his life. Mack's mission was complete," said Jacque Fowler, English's sister.

Mack told the commissioners that he was sorry for the hurt he had caused to the victims, their families and to his mother.

The district attorney argued that Mack remains unpredictable and is still a threat to the public.

"We feel the portrayal by him in this case as an innocent employee who was being wronged by these people… is so far off the truth of what happened... ," said Deputy District Attorney Richard Sachs.

Mack's parole was denied Tuesday and he will be eligible for another hearing in three years.