It didn't take long for investigators to piece together Sherita Williams' last night on Earth.

At 6:05 p.m., on Nov. 28, 2003 - a day before the popular high school junior was found strangled under a bridge on the Camden-Pennsauken border - a video showed her getting her eyebrows done in a Pennsauken nail salon.

Around 6:30, according to records, Williams called a boyfriend in Camden from a pay phone a few blocks from his house.

But in the months that followed, all leads came to a dead end. Most killers know their victims, police say. Williams' death appeared to be random, the hardest kind of case to crack.

On Friday, more than seven years after one of Camden County's most frustrating cold cases began, Williams' parents finally will see the man who killed their daughter sentenced.

Luck, science, and the perseverance of a cadre of professionals from the Camden County Prosecutor's Office and Pennsauken police paid off in March when a classmate of Williams', Warren Dixon, admitted that he choked the outgoing 16-year-old to death because she wouldn't have sex with him.

"We worked hard on this," said Harry Williams III, the dead teen's father. " 'We' is everybody - the media, family, Prosecutor's Office, and friends. Now is the end of the saga."

The sentencing at Superior Court in Camden will be a reunion of sorts.

Over the years, Sherita Williams' father forged a bond with Sgt. Martin Wolf of the Prosecutor's Office.

Wolf, the lead investigator, always listened when Williams, a retired Department of Corrections officer, called to ask about the case or just to talk and cry about his daughter.

Wolf, a former assistant prosecutor, came to feel he had known Sherita Williams. He put more hours into solving the murder than on any other case he has worked in his roughly 17 years in law enforcement.

"It was a case that needed that much time," he said.

John Greer took over as lead investigator in 2008. He was inspired by Williams' loving family, which held annual marches to the 36th Street Bridge where the teenager's body was found.

"It was a breath of fresh air to see someone keep the hope alive," said Greer, who retired from the Prosecutor's Office after Dixon was arrested in January 2009.

When the investigation lagged and Williams felt as though authorities had taken "their shoes off and put some slippers on," he asked for meetings.

The case "was kept alive because that's what we do," said Lt. Frank Falco of the Prosecutor's Office.

But, Falco added, "it was also kept alive because of [Williams'] pushing and pushing."

Next to Sherita Williams' body, police had found a penny and a receipt for a black T-shirt bought at 4:28 p.m. at Modell's in the Cherry Hill Mall on the day after Thanksgiving.

Modell's has surveillance at the register. But on Nov. 28, 2003, the day Sherita Williams was last seen, the camera didn't work.

Wolf and others pulled credit-card receipts from the store and tracked down shoppers they hoped had seen the person who bought the shirt.

Investigators interviewed dozens of people who knew Sherita Williams. They gathered DNA samples of acquaintances in hopes one would match a semen stain found on her jeans.

They talked to people who may have crossed paths with the teenager. A homeless man who hung out under the bridge. A drug addict who lived nearby.

Williams' boyfriend, who was sleeping when Sherita showed up at his house, passed a lie-detector test. His parents had been home that night, and his mother didn't let Williams in.

The Modell's receipt yielded no usable fingerprints. Neither did the penny.

One item, however, offered promise.

A man's hair cap was sent to the state police lab soon after it was retrieved at the crime scene. Investigators had it checked for hair and fibers, but the results were slow to arrive.

In 2007, authorities finally caught a break. Dixon had been convicted on a drug charge and his DNA had been entered into a national database. After four years, investigators found a match for the DNA on Williams' jeans.

Police picked Dixon up at a meeting with his probation officer. He acknowledged that he had known Williams. He had transferred to Pennsauken High from Camden High in 2003, he said, and he shared a class with one of her friends. He said he and Williams had had sexual relations. Officers didn't believe him.

"He was very street savvy," Greer said. "I think he was trying to lay the foundation for any future evidence regarding DNA."

Authorities showed him the cap, but they didn't initially tell him where they had found it. Dixon was noncommittal, though he later said it belonged to him.

When Greer took over the investigation in 2008, after Wolf's Army Reserve unit was activated, Williams wept. He had trusted Wolf, he said. But Greer pressed on.

Exasperated, Greer sent the wave cap to a private lab in Virginia to check for DNA.

"If I could get DNA evidence from the scene itself, that's the coup de grace," Greer said.

Three days later, the results from the test on the wave cap came back from the state police lab and they showed it did not belong to the victim. But authorities didn't have a sample of Dixon's hair. It took about a month to get a court order for the specimen.

At the Prosecutor's Office, where officers took the hair sample, Dixon seemed overly curious about the case.

"What would happen if I did this and it was an accident?" Greer recalled Dixon asking. "Would I still have to go to jail?"

Dixon ended the impromptu interview session on what investigators felt was the brink of a confession.

"He wanted to cleanse his soul at this point, but he was looking for a way out," Greer said.

 Though a lab report in January 2009 found that Dixon's hair was not a match to the hair on the wave cap, authorities felt they had enough probable cause and evidence to charge him that month.

Dixon, now 25, lived near the bridge and likely simply crossed paths with Williams that night, authorities said.

At Dixon's sentencing on Friday, the Williams family plans to talk about Sherita and show photographs that trace her life from the time she was a baby.

"I want the court to know who she was . . . just to watch her grow," Harry Williams said.

Contact staff writer Darran Simon at 856-779-3829 or dsimon@phillynews.com.