Four men in a truck, some weed, an attempted robbery and a single bullet — that’s the combustible mixture that left Leighton Powe Jr. dead in September 2013 and means Felix Adams Jr. will be sentenced to life in prison.

A six-man, six-woman jury in St. Tammany Parish took less than two hours Thursday to return a guilty verdict on three charges levied against Adams: second-degree murder, armed robbery and obstruction of justice.

The murder charge requires a life sentence.

Adams is the second person convicted in the case. Trenton Johnson, who drove the car in which the robbery and shooting occurred, pleaded guilty in October to manslaughter in return for a 25-year sentence. As part of his plea agreement, Johnson testified against Adams on Wednesday.

The basic narrative of what happened wasn’t in dispute during the three-day trial: Johnson, Adams and another man, Bobby Isidore, went to meet Powe behind a Dollar General store on Robert Road in Slidell. The three had told Powe they wanted to buy marijuana but actually intended to rob him.

Johnson was the driver, Isidore was in the seat behind the passenger and Adams was next to him. When Powe got into Johnson’s truck, Isidore was supposed to grab him and Adams was to take the weed.

Johnson testified that he learned Adams had brought a gun along only when they were already on their way to meet Powe.

When Isidore grabbed Powe, a struggle ensued. That’s when Adams shot Powe in the head, spreading blood, “brain matter and possibly skull matter,” Johnson testified.

“I’m quiet, scared,” Johnson said of the moments after the robbery. The three men then drove away with Powe in the truck, still breathing, Johnson said. He told the jury that Adams directed them to a spot on Javery Road, where they dumped Powe’s body in a ditch.

Johnson then left the area with another man, Darion Causey, who took Johnson’s clothes, burned them and told him to report his truck stolen.

A Slidell police officer showed up at his house to take a report on the stolen truck, but then several more officers arrived and took Johnson to the police station. In his third interview with police, Johnson told them he had been there when Powe was shot.

Public Defender John Lindner, who represented Adams, seized on this admission.

“You’ve admitted that your initial story wasn’t the full truth?” he asked Johnson on cross-examination.

“Yes, sir,” Johnson replied.

Lindner also quizzed Johnson about his deal with prosecutors, asking the 20-year-old if he is still facing an obstruction-of-justice charge and if he had to testify against others in the case. “Yes, sir,” Johnson answered each time.

Lindner asked Johnson if he was a willing participant in the robbery.

“Yes, sir,” Johnson answered. He also said he did not try to back out when he saw Adams had a gun.

Adams testified Thursday morning in his own defense, claiming that the gun went off accidentally when Powe swung at him during the struggle in the truck.

“He wanted to tell his story,” Lindner said. “He took responsibility for what he did.”

Lindner said Adams shouldn’t be punished any more than Johnson.

He tried to persuade the jury that they should instead convict Adams on the lesser charge of manslaughter.

Isidore and Causey are set for trial next month. Another accomplice, Ki’Shion Griffin, who allegedly conceived of the robbery and recruited the others, is scheduled for trial in March, as well.

Adams will be sentenced March 2 by Judge Allison Penzato.

Follow Faimon A. Roberts III on Twitter, @faimon.