Barry Gilton and Lupe Mercado, a longtime couple from San Francisco and parents of four, felt they had no other option when they couldn't convince their 17-year-old runaway daughter to leave a life of prostitution and return home. So they shot and killed her pimp, authorities allege.

Now, Gilton, who is accused of shooting and killing 22-year-old Calvin Sneed, faces a potential life sentence. Mercado faces 25 years-to-life.

According to the San Francisco Chronicle, when the couple was unable to get their daughter to leave Sneed of her own accord, they stalked him around the state, finally killing him near Candlestick Park.

But the defense attorney for Gilton says the evidence surrounding the case is circumstantial at best, and claims Sneed was a known gang member who could have been killed by a rival gang.

"The evidence that they perpetrated the act is very slim—there's some circumstantial evidence and they have a motive," says Eric Safire, Gilton's attorney. He says officials haven't presented all its evidence, but says all they have is "a video of a car similar to [one of Gilton's] family member's was seen on the night of the murder."

"There's no weapon, and there's no eyewitness," he adds. "What we do know is that the victim is a known gang member, he was out at 2 a.m. in a high crime area—I can only presume he was engaged in his normal and customary [pimping] activities. He was subject to gang violence."

Phone calls to the San Francisco District Attorney's office from U.S. News were not immediately returned, but a spokesman for the office told the Chronicle that the state has more than circumstantial evidence.

"San Francisco police have thoroughly investigated this case," the spokesman said. "We would not charge a case unless we had a good-faith basis that we could prove the case beyond a reasonable doubt."

Safire doesn't deny the family had a motive to commit the crime.

"There's no doubt the family wanted their daughter to stop seeing Sneed," he says, adding the family contacted local police departments and tried to put her name on a national missing persons list.

"It appears that they did reach out through normal channels to seek assistance," he says. "My impression is that they were told there are budget crises and those kinds of responses are expensive."

According to Safire, Gilton's daughter wasn't with Sneed at the time of the shooting, "but there's some evidence she was on the phone with him and close by at the time."

The Chronicle reports that Sneed was involved in a drive by shooting on May 27 in North Hollywood. Police believe the shooter was either Gilton or Mercado. A week later, he was killed near Candlestick Park in San Francisco.

Although Safire maintains his client's innocence, he says that any parent can identify with what the family was going through.

"She was in some sort of crisis emotionally—the parents felt she was non-communicative," he says. "So far, the responses in the newspaper have been 90 percent positive. I like our chances with a jury."