To hear James Wonder tell it, the moments leading up to when he shot and killed an off-duty federal agent began with him driving to the post office to mail three letters and he noticed a black car tailing him. No matter how much he tried to drive away, the car insisted on following him.

The Miramar retiree made his way on Aug. 5, 2008 into the parking lot of the post office at Pines Boulevard and Dykes Road in Pembroke Pines. As he got out of his car, Wonder said, he saw the black car turn in, park near him and the driver emerged, much larger than him, spewing profanity and getting closer.

Wonder reached for his gun, he said, to scare the man away.

“I think I would have been killed,” Wonder said in Broward County criminal courtroom Monday.

But he also fired, striking off-duty U.S. Customs and Border Protection agent Donald Pettit in the head, killing him.

Wonder and his defense attorneys are trying to persuade Broward Circuit Judge Bernard Bober that he feared for his life and under Florida’s “Stand Your Ground’’ law, the manslaughter charges he faces should be dropped.

“Stand Your Ground” states that individuals who are following the law have no duty to retreat in the face of a threat, and that those individuals may meet force with force if they believe it is necessary to protect themselves or another, or to prevent a forcible felony.

But prosecutors say Wonder was angry and snapped with no reason to fear when he shot Pettit.

Wonder, who turns 70 in a few weeks, faces up to 15 years in prison if convicted.

The day of the shooting, Wonder, who had a concealed weapons permit, was carrying his gun in his waistband.

Ever since he suffered renal failure, followed by years of regular dialysis to stay alive, Wonder said his frame had gotten slighter and he became more inclined to carry a gun to protect himself.

At one point Monday, his lawyers had him stand up to show his slight 150-pound frame, dressed inconspicuously in a yellow shirt, jeans, sneakers and a black wind breaker.

“I feel vulnerable seven days a week,” Wonder said at one point during questioning by prosecutor Michelle Boutros.

That day, as Wonder remembers it, the black car was on his tail and refused to back down. He sped up to get away, but the black car kept following him, getting too close for comfort.

Pettit’s daughter previously said in a deposition that the argument began because Wonder pulled in front of her father’s car and failed to stay in one lane.

Wonder said after he pulled into the post office parking lot, Pettit’s Chrysler followed. Pettit got out of the car and began spewing profanities, Wonder said.

“He was coming at me like a football player,” he said.

Saying he was afraid he was about to be beaten, Wonder reached for his gun.

“I went into some kind of panic mode,” Wonder said, “I had never shot anybody.”

After killing Pettit, Wonder got back into his car and left.

He mailed his letters from another post office and went home. He later tried to get dialysis but was turned away because his pulse was too high.

As the day went on, Wonder saw news helicopters buzzing over the post office scene and heard on the news that the man he had killed was a federal agent. He said he became as scared as he had ever been.

“I figured they were looking to gun somebody down,” he said, later adding “I was scared to death.”

He dismantled the Colt and put it in a plastic bag, although he denied Monday that he was trying to hide it. Wonder said he never threw away anything related to the shooting.

But he did rent an SUV to drive around instead of his own car.

The next day, he drove the SUV to the dialysis center, where he was arrested.