A neighborhood feud or a calculated execution? Trial begins for Chester County man charged with fatal shooting.

At her dining room table in West Goshen, Jill Jennings was working late on invitation designs for her stationery company, she said, when she heard the unmistakable bang of a gunshot.

She knew her husband, George Brooks Jennings, had been outside late that night in August talking with their next-door neighbor, Clayton P. Carter III. For years, the men had clashed, authorities said, disagreeing about everything from politics to lawn decorations to children playing too loudly in the street.

She ran to the living room window, where she had a partially obstructed view of the men. Carter held a .380-caliber Ruger semiautomatic handgun.

Then, she said, she watched in horror for several seconds as Carter stood on top of her husband’s body, which lay motionless on their property line on the 300 block of Box Elder Drive.

“The defendant has the gun pointed at his head,” she said, “and he shoots it.”

Jennings testified Friday in the first day of Carter’s trial before Chester County Court Judge Ann Marie Wheatcraft. Carter, 53, faces charges of first-degree murder, third-degree murder, and voluntary manslaughter.

Earlier in the day, the prosecution and defense laid out their arguments to the jury of eight women and four men.

Assistant District Attorney Vincent Cocco said Carter had planned to end the years-long feud that night, choosing to bring outside the smallest of his guns, the one he could most easily conceal in a sweatshirt pocket, and then placing a knife near Jennings’ body to make it look as if he’d been acting in self-defense.

“What was staged to look like a neighbor dispute gone wrong," he said, “was really a cold-blooded, calculated execution.”

Carter’s defense attorney, Joseph P. Green Jr., said his client had gotten fed up with Jennings’ “campaign” to get Carter to move out of the neighborhood. Carter had called the police about past disputes that Jennings instigated, Green said, but nothing was done.

“Brooks Jennings was the Republican committee person for this precinct," Green said, “and everyone cut him a break.

“To suggest Mr. Carter went looking for trouble is to miss the mark here,” he added. “Ask yourself: How much is a man supposed to take?”

When the shooting occurred early on Aug. 8, Jill and Brooks Jennings and their son, Matthew, then 9, had lived in the two-story Colonial home for eight years. The neighborhood was social, Jill Jennings said, with parents and children getting together every weekend. Her husband, sometimes referred to as “the mayor” of Box Elder, fit right in, she said.

He got along with everyone until about 2013, when Carter moved in to care for his aging in-laws, the Magills, who lived next door, she said. The couple tried to make Carter, his wife, and his daughter feel welcome, she said.

But the relationship soon soured. Police were called multiple times, authorities said, and at least twice Carter brandished a gun, which led Jennings to back down.

Hours before the killing, police had been called to the property for the latest dispute between the men.

Jill Jennings wasn’t home at the time, but said her husband told her about the argument, saying it began when Carter cursed at him while they were in their yards.

She told her husband she was worried, she said, because “repercussions” always followed the men’s disagreements.

Around 9:30 p.m., the Jenningses tucked in their son, she said, and then went downstairs to watch TV. Brooks Jennings, whose blood-alcohol content was 0.198 percent when he died, sipped Canadian whiskey and ginger ale, she said.

Two hours later, the 51-year-old went outside, and his wife said she figured he was working in his shed. Then she heard voices, which she recognized as her husband’s and Carter’s.

Green said his client had gone for a late-night grocery run and was provoked by Jennings upon his return. Jennings had set up a lawn chair by the property line, Green said, and was shining a handheld spotlight in Carter’s direction as Carter tried to park his car.

Jill Jennings said she heard parts of the argument, including her husband asking Jennings to remove a skeleton lawn decoration that scared neighborhood children. Carter refused, she said.

She returned to her work, she said, only to be startled shortly after by the sound of the first gunshot.

After watching the second shot from the window, she said, she called 911 as she ran to help her husband. Carter’s wife and daughter were kneeling on the grass, crying and asking Carter why he had done this, she said. Neighbors began running out of their homes, too, awakened by the commotion.

One was Glen Graham, whose wife woke him at the sound of gunshots, he testified, and he ran outside, where Jill Jennings told him, “Clayton finally shot Brooks.”

Graham ripped off his shirt, he said, and attempted to bandage his neighbor’s bloodied face. Nearby, Graham said, Carter stood, offering no help and saying, “He attacked me, so I shot the [expletive].” Police soon arrived.

At one point, Jill Jennings said, she turned toward her home and saw her son standing at his bedroom window. She motioned for him to meet her at the bottom of the stairs. There, she said, she told the boy, “Go back in the family room and watch TV.”

She promised him, she said, that she’d tell him what had happened as soon as she knew.

Carter, who sat quietly in court wearing a blue shirt and blazer, has been held at the Chester County Correctional Facility since his arrest that night. His trial is expected to last several days.