Sex offender kills teen while under GPS monitoring, police say * Darrin Sanford may face death penalty in fatal beating, stabbing of Alycia Nipp, 13 * Sex offender monitored via GPS, checked in with probation officer day before murder * Experts say GPS creates false sense of security; it's no "magic bullet or panacea" * Aunt says daughters keep asking if angels will bring cousin "Licy" back By Eliott C. McLaughlin and Patrick Oppmann CNN VANCOUVER, Washington (CNN) -- When 13-year-old Alycia Nipp didn't come home from a trip to Wal-Mart, her family had no idea where she was, but a tracking device was transmitting the location of her alleged killer. Alycia Nipp, 13, was a free spirit, her aunt says, and liked to collect neon drinking straws. The quirky seventh-grader, who went by "Licy," could tell you the origin of every neon drinking straw in her collection and she "sewed buttons on everything," said her aunt, Amber Hager. Her family thinks her free-spirited nature may be the reason she walked through a field popular with transients -- a field she'd been warned to stay away from and where her body was found February 22. Licy's family had reason to be cautious. Hager was raped twice as a teen and Licy's grandmother was kidnapped as a child, Hager said, so the family was extra vigilant with Licy and Hager's young daughters. "We all made Licy the promise that it would never happen to her. The cycle would end," said Hager, who is acting as family spokeswoman. "Now we're left wondering: What didn't we say? What didn't we do? How come she didn't listen?" Darrin Sanford, 30, was one of several homeless people living near the field in an abandoned home slated for demolition, police said. He was convicted in 1998 of communicating with a minor for immoral purposes and luring minors with sexual motivation; he was sentenced to probation, said a Clark County sheriff's report. When he was released from jail in January, following a November probation violation, Sanford was fitted with a global positioning tracking unit on his ankle, according to the Washington Department of Corrections. Sanford was wearing the device seven weeks later when he tried to rape Licy before beating and stabbing her in a field a couple of blocks from the street where she lived, according to police. Authorities said they used GPS to corroborate Sanford's confession. A Clark County judge this week postponed his arraignment until June so the defense and prosecution can prepare for death penalty arguments. Sanford's defense attorney Michael Foister declined to comment on the allegations against his client. Debate over GPS The slaying rocked the enclave of Hazel Dell in Vancouver, a 15-minute drive from Portland, Oregon, and serves as fodder for those who claim GPS is used too broadly and bluntly as a tool for keeping tabs on offenders. "They can't monitor it live, and even if you could monitor it live, him being in the field wouldn't have told you [if] he was murdering the girl," said Evan Mayo-Wilson, an Oxford University lecturer who has studied the use of GPS. There are two types of GPS monitoring: active, in which the offender's whereabouts are surveyed in real-time, and passive, in which probation or parole officers check an offender's movements after the fact. Sanford was passively monitored, said Anmarie Aylward, the Washington DOC's program administrator. Both types of GPS are important tools for law enforcement, Mayo-Wilson said, but the technology must be coupled with other efforts to reduce recidivism, including treatment programs, personal visits and interviews with neighbors, family members and employers. Sex offenders should be assessed on a case-by-case basis, and supervision programs must be based on fluid assessments that weigh the likelihood of reoffense, said Peter Ibarra, a sociologist at the University of Illinois-Chicago who studies the use of GPS in stalking and domestic violence cases. "You have to use it very responsibly," Ibarra said. "It's a technology that cannot stand alone, especially if you're thinking about using it with offenders who imperil the public." Sanford was registered as a Level 3 sex offender, the category considered most likely to reoffend, according to the Clark County Sheriff's Office. He was listed as homeless on the state sex offender registry, one of 34 transient sex offenders in Clark County. There are eight homeless Level 3 offenders registered in Clark County. Sanford was living in a vacant home near an overgrown field where Licy's parents sometimes played paintball. The field, littered with trash, has "No Dumping" signs along its periphery and is buttressed by fast-food joints, Chinese restaurants and strip malls. The air smells of frying oil. Resident Nick Holden, whose daughter was Licy's friend, told The Oregonian newspaper that the field was a popular shortcut -- "a kid highway." Though it wasn't necessarily deemed unsafe, he told the paper, "you ask the kids to not go alone." Licy was told just that, but on February 21, as she and a friend returned from Wal-Mart, Licy said she wanted to cut through the field. Her friend declined, Hager said. Police: Sanford unsure of his weapon Sanford told detectives he met Licy near the vacant homes and walked with her to an isolated area of the field, police said. There, he attempted to have intercourse with her "but wasn't able to complete the sexual act," according to the probable cause affidavit filed in court. "After she giggled at him," continued the affidavit, "he was overcome with a violent rage and hit her with something in the back. She turned to face him and he kept hitting her, knocking her to the ground."