Claims of self-defence by the man who killed former Saskatchewan Roughriders player Joe McKnight withered under scrutiny, a prosecutor told jurors Friday, but a defence lawyer insisted the shooter fired as McKnight approached his car, spewing obscenities and threats, following a traffic confrontation in December 2016.

The conflicting claims were made in opening statements in the second-degree murder trial of Ronald Gasser, 56.

Defence lawyer Matthew Goetz said authorities in suburban New Orleans were under political pressure to make an arrest when Gasser was jailed days after the shooting. Goetz alluded to racial unrest that year in American cities, including the St. Louis area and Baton Rouge.

Gasser is white; McKnight was black.

This undated file photo released by the Jefferson Parish Sheriff's Office shows Ronald Gasser, accused of killing former NFL running back Joe McKnight during a road rage dispute. (Canadian Press)

Seth Shute, an assistant District Attorney in Louisiana's Jefferson Parish, acknowledged that Gasser was initially freed after the shooting. But Shute said Gasser was arrested after investigators talked to numerous witnesses and assembled physical evidence contradicting Gasser's claim that McKnight, 28, had tried to lunge into his car through a passenger window after both vehicles stopped at a busy intersection.

Jurors were selected Tuesday. Opening statements were delayed because unusually frigid winter weather in south Louisiana prompted a two-day closure of the parish courthouse in the New Orleans suburb of Gretna.

'Mobile shouting match' starts on bridge

Shute said jurors will hear from dozens of witnesses. Some will testify about what Shute called a "mobile shouting match" that began on a bridge spanning the Mississippi River in New Orleans and continued into neighbouring Jefferson Parish, Shute said. Others will talk about hearing the pop-pop-pop of three gunshots, seeing McKnight fall and watching as Gasser exited his car with his handgun still smoking.

Jurors also will hear a police officer recount Gasser's first words at the shooting scene: "He cut me off and got out on me."

McKnight drove his grey SUV aggressively that afternoon, Shute acknowledged. There was a small amount of marijuana in his system and a "therapeutic dose level" of Oxycodone in his system, he added, having noted that McKnight was training in hopes of returning to the NFL after an injury cut his pro career short.

But he said there was no gunpowder residue on McKnight, indicating he was not shot at the close range Gasser had indicated.

And an examination of the wounds indicated that McKnight's hands were resting on the window of Gasser's car, with no sign that he had aggressively moved to get inside.

Defence, prosecutor paint two different pictures

"His version of events does not match the physical evidence," Shute said.

But Goetz countered that, "Ronnie believed he (McKnight) was coming after him."

He also claimed that, McKnight "was trying to kill" Gasser by running him off the road in traffic, before the shooting.

McKnight played three seasons for the New York Jets and one with the Kansas City Chiefs, during his time. He spent a season in the Canadian Football League, playing two games for the Edmonton Eskimos and three for the Saskatchewan Roughriders.

He was shot Dec. 1, 2016. Gasser never left the shooting scene and was initially freed after more than eight hours of questioning — which Shute said jurors will see.

Sheriff denies race played a role in case

Gasser's release sparked protests, and some said race played a role in his release. Jefferson Parish Sheriff Newell Normand, who has since retired, angrily denied that race played any role in the case. He recounted a painstaking investigation with more than 160 interviews.

Arrested on a manslaughter charge four days after the shooting, Gasser was indicted by a grand jury on the second-degree murder charge in February. If convicted as charged he would be sentenced to life in prison.

The trial is expected to last well into next week, with state District Judge Ellen Kovach presiding.

The case echoes another New Orleans-area road-rage shooting from 2016. Former New Orleans Saints star Will Smith was gunned down that April. The shooter was later convicted of manslaughter and sentenced to 25 years.