02/11/2014 06:43 pm ET Updated Mar 27, 2014

New Person Of Interest In Disappearance Of Sheila Lyon And Katherine Lyon

A convicted child sex offender has emerged as a person of interest in the presumed killings of two young sisters who vanished from a suburban Washington shopping mall nearly 40 years ago, Maryland police said Tuesday.

Chief J. Thomas Manger with the Montgomery County Police Department announced at a press conference that Lloyd Lee Welch, also known as Michael Welch, is now the primary person of interest in the 1975 disappearance of 12-year-old Sheila Lyon and her 10-year-old sister Katherine. Welch is the second convicted sex offender to emerge over the decades as a target of investigators on the case.

The disappearance of the the Lyon sisters sparked widespread media coverage in the years since their disappearance. Both are presumed dead, though extensive searches over the years have failed to lead to their bodies.

Manger said Welch was identified as a suspect during a recent reexamination of the cold case file. The chief declined to elaborate and wouldn't say why Welch wasn't investigated sooner.

"I'm not going to talk about how we got any information," Manger said.

The Lyon girls' disappearance is rooted in the events of March 25, 1975.

At about 11 a.m. that day, the girls left their Kensington home and walked to nearby Wheaton Plaza, a popular suburban shopping center. Wheaton Plaza is now the Westfield Wheaton mall.

The Lyon sisters were off school for spring break at the time and wanted to look at Easter exhibits in the mall. They had about $4 between them.

According to a March 25, 1980, article in The Washington Post, the girls were told by their parents, prominent radio disc jockey John Lyon and his wife Mary, to return home by 4 p.m.

At about 2 p.m. that day, the girls were spotted by witnesses at the Orange Bowl, a pizza shop that was part of a popular chain at the time. What happened to them after that remains a mystery.

According to Manger, authorities have placed Welch at the shopping center on the day the girls disappeared.

"Investigators have established the fact that Welch was at Wheaton Plaza on March 25, 1975," the chief said. "They've also established that Welch was observed paying attention to the Lyon sisters while at Wheaton Plaza."

CASE PHOTOS: (Story Continues Below)

The Lyon Sisters

Manger said Welch, a 57-year-old convicted sex offender, has "multiple convictions for sexual offenses against young girls" in Virginia, South Carolina and Delaware. He has been incarcerated in Delaware for one of those offenses since 1997.

According to the Delaware Department of Corrections website, Welch is locked up at the James T. Vaughn Correctional Center in Smyrna, Del. He is scheduled for release in June 2026.

Welch was previously employed by a traveling carnival that often set up at shopping malls, police said Tuesday. That job, police said, took Welch all over the country during the 1970s, '80s and early-'90s.

Welch traveled with his girlfriend, a coworker at the carnival identified by police as Helen Craver. Authorities said Craver is deceased.

Investigators asked that anyone with any information about Welch, Craver or an unidentified man who worked as a security captain at Wheaton Plaza at the time of the girls' disappearance, to contact them.

"We believe [information about them] could help us fill in some of the blanks and assist us in determining more information about Mr. Welch," Manger said.

Steve Vogt, special agent in charge of the FBI in Maryland, said authorities also would like to speak with possible sex crimes victims of Welch who have not come forward.

"We understand we’re asking people to think back several decades to remember details they may not think matter. However, the information you provide could be vital in our search for evidence and put to rest difficult questions for the Lyon family and for any other victims who may exist," Vogt said.

For all the uncertainty in the case, the Lyon sisters’ family said it remains hopeful the case will one day be solved.

"Throughout these years, our hopes for a resolution of this mystery have been sustained by the support and efforts of countless members of law enforcement, the news media and the community," the family said in a statement released by police Tuesday. "The fact that so many people still care about this case means a great deal to us."

Tuesday is not the first time police announced a possible sex offender connection in the case.

In March 1987, Montgomery County Police Detective Bill Campbell told reporters that police were following their "most promising lead" in the investigation. Campbell said investigators believed the girls' disappearance was linked to convicted sex offender Fred Howard Coffey Jr.

Coffey, the detective said, had been near Wheaton Plaza when the girls vanished.

"His activities and whereabouts ... are not at all clear," Campbell said of Coffey, according to a March 1987 report by The Washington Post.

Detectives were ultimately unable to link Coffey to the Lyon girls. The 68-year-old convict is currently serving a life term in North Carolina for the 1979 murder of a 10-year-old girl.

Anyone with information in the sisters' case is asked to call investigators at 1-800-CALL-FBI. Tips may also be submitted online at