Her child's innocence is a pleasant memory for Samano, far from the cruel reality that became the last moments of Diana Hernandez's life.

Diana disappeared on April 2, 1994, a day before Easter. Her body was found the next day in a trash bin inside a cardboard box in the apartment complex where she lived. An autopsy indicated she was suffocated. Police said she was sexually assaulted.

In the 15 years that have passed, Diana's two sisters, one of whom was her fraternal twin, graduated from high school and got married.

Every time one of Samano's daughters hit a life milestone, she couldn't help but think how Diana's life would have unfolded if she were alive.

"There's not one day I don't think about her," Samano said Monday, holding back tears. "If she was alive, she'd probably be married or going to college."

Later Monday, she was relieved to learn that the slaying might have been solved, that Las Vegas police had arrested a sex offender who they believe is responsible for the 7-year-old girl's death.

Detective Stephen Popp said 36-year-old Greg Wallen was arrested without incident outside a relative's house in Pahrump.

Wallen, who lived in the same building as Diana at the Sandpiper Village Apartments, 3955 Algonquin Drive, near Flamingo Road and Maryland Parkway, was one of dozens of volunteers who helped search for the girl the day she went missing.

"It was a crime of opportunity for him," Popp said. "He's a pedophile."

Popp said advances in forensic technology led to the breakthrough in the case.

"A lot of good detectives looked at this case over the years and were not able to solve it," Popp said. "Without DNA, I don't know if we'd be able to get this far."

Popp would not specify what linked Wallen to the incident. But he said Wallen was positively identified through DNA recovered on Diana's body, and physical evidence found in the trash bin.

The gruesome crime horrified the community. Some parents were frightened to let their children play outside. The MGM Grand offered a $10,000 reward to anyone with information resulting in the arrest and conviction of the person responsible for Diana's death.

Popp said the investigation was a high-priority case for detectives who combed through the file year after year. He described the unsolved slaying as disturbing because it involved a child.

"For those of us who have children, obviously, it sort of hits home," Popp said. "They are true innocent victims."

Wallen was not a suspect initially. He appeared on detectives' radar in January when detectives realized a man who has since become a registered sex offender had lived in close proximity to the victim's family at the time of Diana's death.

He had not yet been convicted in a 1992 incident involving a 4-year-old girl when Diana went missing.

Popp said residents of Diana's complex in 1994 were not aware they lived next to a potential sex offender.

Popp said Wallen's conviction from the 1992 incident was "eerie" because it was so similar to Diana's case.

Wallen served several years in Nevada prison for a lewdness with a minor conviction stemming from the 1992 incident in Nye County, said Detective David Culver.

The Metropolitan Police Department's full-time cold case section includes Popp and two other detectives.

Popp said all three collaborated in the case and aided in the arrest. He said that in the 15 years the case remained unsolved, at least eight detectives investigated the case. At least four of them have retired and one has died.

Popp said the initial investigation involved hundreds of law enforcement personnel, including those from the Police Department's Missing Persons Detail and University of Nevada, Las Vegas police. About 40 volunteers helped police search the area hours after Diana's disappearance.

Samano and two of her daughters, now 23 and 22, reflected on Diana's death Monday at a family home in North Las Vegas.

Samano took Diana and Diana's twin sister, Adriana, and older sister, Stella, toy shopping at a nearby strip mall the day Diana went missing. Diana had run ahead of her mother and sisters as Samano stopped by the apartment's office to pay rent.

Adriana Hernandez, now 22, was emotional about the arrest. She said she felt a lot of guilt because she and Diana were racing shortly before Diana disappeared. She stopped running, and stayed back with her sister, Stella, while her mother paid rent. Diana ran up to the apartment.

"I felt like it was my fault," Adriana Hernandez said Monday, with tears streaming down her face. She said her sister's brutal slaying hit her especially hard because they had a tight bond only twins can have.

"I'm able to live with it, but it's always in the back of my mind," she said. "Even though I was young, it affected me a lot."

It was presumed Diana was abducted near her front doorstep. Samano and Diana's two sisters said only between five and 10 minutes passed between the time they last saw Diana and when the rent was paid.

Popp said there still are a lot of questions that remain regarding what happened after Diana was abducted. Police didn't initially find her body in the trash bin even though the apartment complex was thoroughly searched the day of her disappearance.

That prompted theories the killer was in the area and had waited to place her body there overnight before the search resumed.

"Forensics tells us he's the guy," Popp said of Wallen. "As far as a timeline with where he was, what he did, how he committed this crime, I can't tell you that."

Popp wouldn't comment on any statements Wallen made to police after his arrest Monday.

Wallen was detained on a murder charge at the Clark County Detention Center. His initial court appearance is scheduled for Wednesday.

Diana's family expressed relief over the arrest. They said they now have closure.

But Samano said she is also plagued by mixed emotions.

"I feel anger. I feel sad. It's like I want to kill him myself," Samano said. "But I know she's in heaven right now.

"Her life is no longer a mystery."

Contact reporter Antonio Planas at aplanas@reviewjournal.com or 702-383-4638.