Testimony was set to begin in San Francisco Superior Court Friday in the preliminary hearing of the parents of a teenage girl who fatally shot a man who was allegedly pimping their daughter.

In what promises to be an emotional hearing, Barry Gilton, Lupe Mercado, Antonio Gilton and Alfonso Williams will be in the courtroom on charges they killed Calvin Sneed in the city's Bayview District in June 2012.

Sneed was shot in the head while he was driving near Meade and Le Conte avenues in San Francisco's Bayview District. He crashed into a parked car and died at a hospital later that morning.

Prosecutors say the longtime couple, who are not married but have four children, shot Sneed after learning that their 17-year-old daughter had become a sex worker in the Los Angeles area and that Sneed was her pimp.

The attorneys for Mercado and Gilton have continued to deny that their clients were guilty of shooting Sneed.

"The prosecution has provided insufficient evidence," Eric Safire, Gilton's attorney, said outside of court.

Safire and Mercado's attorney, Tony Tamburello, have argued that Sneed's ties to a Los Angeles-area gang were enough of a motive for someone else to have shot him.

" District Attorney George Gascon says that as a parent he sympathizes with Mercado and Gilton's frustration as parents that their daughter had been victimized, but he said that their tragedy did not make them above the law.

"Vigilante murder is still murder," he said. "We cannot afford to live in a society where people take the law into their own hands."

According to the criminal complaint against the couple, they allegedly traveled to Southern California and, on May 27, tracked Sneed down to a street in North Hollywood where Gilton fired a 9mm handgun at him, striking him. He survived that shooting.

Sneed then traveled up to San Francisco to get the pair's daughter, who had returned to the city, and on June 4 the couple found him again, prosecutors said.

Gilton then allegedly fired again at Sneed, fatally wounding him, according to the criminal complaint.

Gilton and Mercado have been held on $2 million bail each.