CENTENNIAL, Colo. -- Prosecutors say 23-year-old Sir Mario Owens, the accused triggerman in the slaying of a witness and his girlfriend, lived by the motto "You snitch, you die."

During opening statements in Owen's first-degree murder trial on Tuesday, prosecutors said Javad Marshall-Fields told friends less than 24 hours before his death that he feared for his life.

Owens is currently serving a life sentence in the death of Gregory Vann at Lowry Park in Aurora on July 4, 2004.

Marshall-Fields was scheduled to testify in the Vann slaying case. He was a friend of Vann and identified Owens as the triggerman.

About a year later, he was driving through Aurora with his girlfriend, Vivian Wolfe, when they were hit by a hail of bullets. Prosecutors said Owens fired those bullets.

Marshall-Fields confided to friends that he knew he wouldn't live to testify after a $10,000 bounty was put out on his life.

"They're going to kill me. I'm going to die," friends said he told them 24 hours before he was gunned down.

His family was in court as prosecutors played an audiotape of Marshall-Fields talking to detectives about the Vann shooting. Prosecutors said he was warned by Owens' friend not to testify and was offered a $10,000 bribe to stay silent.

"I have to (testify).Greg would have done for me," Marshall-Fields had said.

"It was comforting to hear his voice. But it also reminds me how lonely and empty my life is without him," said Marshall-Fields' mother, Rhonda Fields. "But to know that even in his death, he's still speaking out about what he saw ... and the things I heard, it was just amazing the kind of young man he was."

She has waited for this death penalty trial for nearly two years.

"It's just hard to know that evil is out there, among us," she said.

Prosecutors decided to pursue the death penalty against Owens, arguing that the murder was a calculated, premeditated plan to silence a witness.

Owens' defense attorney said that the case against him is based on a cast of questionable characters. The defense argued that the prosecutor cut plea deals with "questionable witnesses" to get them to say what he wanted.

It was "evidence ignored, evidence overstated, evidence for sale," the defense attorney said.

After opening statements, jurors heard from the first person at the shooting scene, who was unable to resuscitate either victim.

Security was tight for the trial, with metal detectors set up outside the courtroom, in addition to the standard metal detectors at the courthouse entrance. There was also heavy security presence inside the courtroom.

The trial is expected to last 10 weeks. If jurors find Owens guilty of murder, they will then decide whether or not he will face execution.