A new clue into the 1972 disappearance of two boys on an orphanage camping trip in Burlington County has authorities digging deeper to solve the cold case.

Until recently, relatives did not know whether Steven Soden, 16, was dead or alive.

"We were hoping that he was still alive," said Soden's sister, April Leonard, 56, of Sekiu, Wash., who had given a DNA sample to police to see whether it matched any remains of unidentified victims of the serial killer John Wayne Gacy.

Instead, the DNA matched four bones found at Bass River State Park in 2000.

"I didn't want to believe it. I didn't want it to be true. But I feel like he's at peace now," Leonard said Wednesday.

However, she and her family have many questions. How did Steven die? What happened to his companion, 12-year-old Donald Caldwell?

Detective Sgt. Stephen Urbanski of the New Jersey state police said a search with dogs trained to track bones will be done in the Pine Barrens to look for other remains.

"Right now, we need to find Donald Caldwell," Urbanski said, adding that he hopes relatives come forward with information or to provide DNA samples to check against other unidentified remains. Investigators believe Caldwell was one of seven siblings from North Jersey. Urbanski said the orphanage has closed and its records are missing.

"This is a unique case. Look at how long it's been and how far along we have come with DNA evidence," Urbanski said. Finding Caldwell "would definitely be a big break in the case. We don't know whether he's alive."

In 2011, the Cook County (Ill.) Sheriff's Office launched an effort to identify eight victims whose remains were found in Illinois and believed to be among 33 victims of Gacy. Gacy was convicted, and in 1994 was executed.

Soden's half-brother, Ronald, said he contacted investigators in Chicago and told them that when he returned from serving in Vietnam, he learned that his mother had put his brother and sister into an orphanage and that Steven apparently had run away.

"We were thinking, this is a Gacy-type victim, a kid hitchhiking who didn't know anybody," Cook County Sheriff Tom Dart said.

Last year, relatives provided DNA samples to Cook County investigators to determine whether Steven Soden was among the unidentified victims of the serial killer.

Testing by the University of North Texas Center for Human Identification determined that the DNA did not match any of Gacy's victims. In December, there was a match with the Bass River bones.

"When the final word did come, it was hard, it was quite a shock," Ronald Soden said. "He was a young boy, and we always hoped we would hear from him."

Leonard recalled a sad childhood. Her father died when she was a baby, and her mother struggled to care for her and her brother. They bounced among relatives in Pompton Lakes and Paterson in North Jersey.

When her mother could no longer care for the children, she placed them in the Paterson Orphanage, hoping to get them back when she found a suitable home, Leonard said.

The siblings did not like the orphanage, she said. Her brother was quiet, mostly a loner, who struck up a friendship with Caldwell.

In 1972, 18 children and four adults from the orphanage went on a weeklong camping trip in Burlington County.

Steven Soden "had mentioned that he was going to run away, but I never believed he would," said Leonard, who was 13 at the time. "I asked him to take me and he said no. He said I was too young, and that I needed to stay there for my mom. He had no plan."

On that day, April 3, she did not realize how serious Steven Soden had been.

"The boys decided they were going to play hide-and-seek. And the boys just took off and never came back," Leonard said. It wasn't until bed check that the adults realized they were gone, she said.

Investigators searched the woods but found no evidence. There had been a report of boys seen hitchhiking in the area, which led to speculation they had left the area.

When the four bones and a sneaker were found in 2000 in the park by an off-duty trooper, investigators were unable to identify the remains. The DNA profile was entered into a national law enforcement database.

Leonard, now married with four children ages 17 to 35, said her family had hoped Steven would return. Her mother died several years ago.

"She had talked about Steven, how she wanted him to call. She had hoped that he was still alive," Leonard said.

New Jersey state police detectives and the National Center for Missing and Exploited Children are investigating the disappearance of the boys and looking into the Paterson Orphanage group.

Anyone with information is asked to call the center at 1-800-843-5678.

Contact Barbara Boyer at 856-779-3838, bboyer@phillynew.com, or follow on Twitter @bbboyer.

Inquirer staff writer Joseph A. Gambardello contributed to this article, which also contains information from the Associated Press.