Darlene Washington sat on a swivel chair bouncing her great-grandson on her lap while his estranged parents visited her East Liberty home.

It was then that she realized her grandson — the boy’s father — was armed.

“I looked up, and I saw that he had a gun, and all of a sudden, it went off,” Washington told a jury Tuesday. “When I turned around, he was shooting her. I couldn’t stop him.”

Police said Terrence Washington fired seven shots, four of which fatally struck Makeida Thompson, his ex-girlfriend and the boy’s mother.

Before her grandson fled, Washington told a jury, he said only, “‘That’s what you get for messing with me.’”

A month after the Nov. 10, 2020, shooting, Washington, 40, was arrested in Seattle. His trial for criminal homicide before Allegheny County Common Pleas Judge Beth A. Lazzara, began Tuesday.

Washington’s mother, Tirzha Moore, and grandmother were the first two witnesses called for the prosecution. Deputy District Attorney Ryan Kiray praised them for testifying.

“It’s remarkable for them to tell the truth — that their own flesh and blood executed someone,” Kiray said.

Both women described the scene that morning — and the shock they felt when Thompson, 32, of Clairton was killed.

“She didn’t do anything. I heard nothing,” Darlene Washington said. “She was talking to me.”

Moore, who was in the kitchen when the shots were fired, described them as ear-piercing. She immediately fell to the floor.

“I was in shock. I was numb,” Moore said. “It should have never happened. She deserves to be here to raise her kids.”

At first, Moore said on cross-examination, she thought Thompson would have been the one to have fired a gun. Thompson was a juvenile probation officer, and Moore said they knew her to carry a concealed firearm in a holster.

“I knew she always had hers,” Moore said.

Both sides agreed in their opening statements that the case is not a whodunit.

Kiray told the jury that Terrence Washington was angry at Thompson for seeking child support and custody of their son.

She had filed a protection-from-abuse petition against Terrence Washington just five days earlier, Kiray said, prompting angry text messages.

“‘That’s the last time you’re going to say child support and custody to me,’” Kiray quoted from one message.

That morning, he said, Washington asked Thompson to meet him at his mother’s house.

“Makeida Thompson was wary of the meeting,” Kiray said. “She even asked the defendant if it was a setup.”

Kiray said neither Moore nor Darlene Washington saw Thompson’s gun that morning. And it was only after she had been killed that a first responder noted it.

“On Nov. 10, 2020, the defendant executed Makeida Thompson in front of his grandmother and 1-year-old son, with his mother in the next room,” Kiray said.

He asked the jury to find Washington guilty of first-degree murder.

But defense attorney Thomas N. Farrell told the jury it was self-defense.

“My client thought he was going to die that day,” Farrell said.

The text messages included one from Thompson, Farrell continued, in which she told his client, “‘I’m going to kill you.”

“She had a gun. She had threatened him,” he said. “He shot her to stop her.”

His client had no intent to kill Thompson that day, Farrell said, which is a required element for a murder conviction.

Farrell also told the jurors that Washington would never have planned to kill Thompson in front of his mother and grandmother, who he knew would tell police the truth.

“That was the worst place to kill her,” he said.

The trial is scheduled to resume Wednesday.