The key prosecution witness to a shootout that left the son of a Canadian diplomat dead and his brother facing murder charges described running for his life from the chaotic scene, newly published video shows.

In the video of his police interrogation in Miami aired by NBC 6, Robert Sanchez admits to brokering the alleged drug deal that brought Jean Wabafiyebazu, 18, to the dingy apartment March 30.

Police allege that Wabafiyebazu went inside bent on ripping off the dealer, Anthony Rodriguez, while his 15-year-old brother Marc Wabafiyebazu waited in their mom's car outside. At some point, gunfire erupted, leaving the older sibling and another teen, Joshua Wright, 17, dead.

"I don't know what happened, officer," an emotional Sanchez tells the detective hours after the shooting. "I just really don't know."

Sanchez, who was not charged, said Jean Wabafiyebazu, a recent arrival in Florida, had bugged him to find marijuana. He said he had finally been able to put the Ottawa teen in touch with Rodriguez, who was shot and wounded in the gunfight.

"One of them was saying, 'The money, the money, where is the money?' And the other one was saying, 'I have the money right here'," Sanchez said.

The situation apparently went awry because Wabafiyebazu had thought he was getting two pounds of pot -- known colloquially as two plates -- but it appears Rodriguez had only one.

"He was expecting to get two plates?" the detective asked.

"Yeah," Sanchez said.

"But you only see one plate?"

"I only saw one," Sanchez said. "They were arguing back and forth about the one plate."

Sanchez said he was playing with his phone thinking everything was basically fine with the deal when the shooting suddenly occurred, prompting him to flee in panic.

"When I heard the gun shots. I just left. I literally just jumped over somebody's fence and I left," he said. "I was scared. I didn't want to get shot."

Marc Wabafiyebazu, who only entered the apartment after the shooting erupted and never fired at or threatened anyone, is charged with felony first-degree murder.

The offence requires him to have been part of what police say was the armed robbery of Rodriguez. Police say Wabafiyebazu confessed to a rookie officer that his older brother planned the robbery and had carried out such drug rip-offs before but this one went sour.

Wabafiyebazu was refused bail in May and remains in custody pending trial, tentatively set for the end of the year. He has pleaded not guilty.

His lawyer was not available to comment. His mother, Roxanne Dube, Canada's consul general in Miami, would not discuss the case.

Rodriguez, 19, who has pleaded not guilty to third-degree murder, claims to have been unarmed. He turned himself in later that day.