Felix Adams Jr. is either a cold-blooded murderer who took concerted steps to hide the evidence after killing a man during a botched robbery, or he is a scared 20-year-old who had never been in trouble before and made one life-shattering mistake.

Those competing narratives kicked off Adams’ second-degree murder trial Tuesday morning in a St. Tammany Parish courtroom.

Wearing a white button-down shirt, tie and gray slacks, the baby-faced defendant listened as attorneys made their opening statements and the first witnesses took the stand.

Prosecutor Julie Knight told the jury of six men and six women that Adams helped plan the Sept. 7, 2013, robbery of Leighton Powe Jr., a robbery that ended with Powe shot dead and his body dumped in a ditch along Javery Road in Slidell.

Knight told the jury that Adams and two other men, Trenton Johnson and Bobby Isidore, met Powe behind a Dollar General store in Slidell. Ostensibly, the three were there to buy marijuana from Powe, but they planned to rob him instead, Knight said. The men referred to the robbery as a “lick,” Knight said, and Adams knew exactly what he was involved in.

“The plan was, when Leighton Powe got in the truck, Bobby Isidore would hold him down, Felix Adams would show his gun and they would take his weed,” she said.

But the plan went wrong, and Adams shot Powe, she said. Then, Adams took over, Knight said, leading his accomplices to where they would dump the body and trying to get rid of the victim’s truck by setting it on fire.

Public defender John Lindner countered that there was a struggle inside the truck and the gun went off accidentally. He said the gun was a rusty old .38 with just one bullet in it, hardly the kind of weapon someone would bring if he were really planning to shoot someone.

“This is a tragic case,” he told the jury. “I am going to put that right on the table.”

But, he said, Adams was a good kid who was working two jobs and found himself in a bad situation.

“You are going to see how inept they were at trying to destroy evidence,” he told the jury. “Mr. Adams was very remorseful.”

Certainly, Lindner said, Adams is no more guilty than the others involved in the crime, especially Johnson, who pleaded guilty in October 2013 to manslaughter and got 25 years. He is expected to testify against Adams.

Adams is facing a mandatory life sentence if convicted of second-degree murder.

“These were three scared, terrified kids,” Lindner said.

The jury also heard testimony from Powe’s father, Leighton Powe Sr., who said that he and his son were supposed to go fishing earlier that day. The younger Powe worked at the Florida Marine Shipyards with his father. “He was real intelligent, inquisitive,” his father said, his voice choking.

Further testimony came from the man who discovered Powe’s body, and the two deputies who responded after it was found.

Powe’s body was face-down in a ditch, partially obscured by vegetation. He was wearing a black T-shirt, red shorts and red shoes.

As witnesses described the discovery, members of Powe’s family wept in the courtroom.

The trial is expected to last until Thursday or Friday. Adams also faces counts of armed robbery and obstruction of justice.

Isidore, the other alleged accomplice in the murder, is scheduled for trial in March.

Another man, Darion Causey, has been charged with obstruction of justice and being an accessory after the fact. His trial also is scheduled for March.

And Ki’Shion Griffin, another suspect accused of being involved in planning the botched robbery, is scheduled for an April trial on a count of second-degree murder.

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