WILLIAM LAWLER didn't want to shoot the man who threatened his girlfriend and him with a 13-inch knife Sunday outside a Pathmark store near his Northeast Philadelphia home.

But even after Lawler, 38, an Army veteran and longtime firearms instructor, showed his 9 mm Glock, the knife-wielding madman didn't want to back down.

"At least a half-dozen times, I ordered him to stop. The last time, I said, 'I don't want to shoot you, but I will,' " Lawler said yesterday, recounting the bizarre run-in outside the supermarket, on Frankford Avenue near Megargee Street in Holmesburg. "Then, after I shot him, he fell to his knees and tried to throw the knife at me."

Lawler, a former school vice principal who still works as a firearms instructor in addition to substitute teaching, said he and his girlfriend had gone to the Pathmark about 5:30 p.m. As they were walking in the parking lot, he spotted the other man - identified by police sources as Dondi DeCosta, 37, who lives near the store - standing with his SUV door open.

"He looked odd from the beginning," Lawler said of DeCosta.

Lawler, who retired from the Army as a lieutenant after serving more than a decade, continued to walk with his girlfriend. DeCosta brandished the knife and started mumbling and cursing at them, Lawler said. Right away, Lawler said, he moved his girlfriend away, unholstered his gun and held it at his side.

"Nine times out of 10, all the gun owner has to do is show the firearm, and the threat goes away," he said.

Not this time: DeCosta instead moved toward the pair, Lawler said, threatening, "I'll cut you up." When he got within 5 or 6 feet, Lawler said, that was it. Lawler leveled the Glock and fired once, hitting DeCosta in the groin.

"My intent was to stop him, not kill him," Lawler said yesterday. "I hope he's OK, and hopefully he will be prosecuted."

DeCosta was taken into police custody as soon as officers arrived, and was taken to Aria Health's Torresdale hospital to be treated for his injuries. He remained there yesterday in critical condition, police said. The man, who has 21 prior arrests on charges including assault and theft, was expected to be charged with aggravated assault and related offenses for threatening Lawler and his girlfriend.

Surveillance video at the store captured the incident, police sources said, and shows that Lawler tried to defuse the situation and to move away before resorting to shooting.

Last week, at a Pathmark in the Northeast's Burholme section, a man was stabbed in the neck and face. That incident had no bearing on Lawler being armed, he said: Since his military days, the Northeast Philadelphia native has had a permit to carry a firearm and has exercised his right to do so.

"I firmly believe that in order to maintain a free society, people need to take personal safety into their own hands," he said. "You should walk around ready and able to protect yourself and others in your community."