Finally, now, one person officially has been accused of being responsible for the preteen sisters' abductions and deaths: Lloyd Lee Michael Welch Jr.
A Virginia grand jury has indicted Welch, currently in a Delaware prison, on two counts of first-degree felony murder, Bedford County, Virginia, Sheriff Mike Brown announced Wednesday in Maryland.
The bodies of Katherine, 10, and Sheila, 12, have not been found. But authorities said evidence and testimony gleaned in the past two years indicate that Welch, a convicted sex offender, abducted the sisters and killed them.
Some portion of the crimes were committed in Bedford County, a roughly 200-mile (322-kilometer) drive southwest of the girls' Maryland home, said Bedford County commonwealth's attorney Randy Krantz, who declined to disclose the evidence.
Authorities said the investigation will continue and didn't rule out others being charged in the case. One of Welch's relatives was indicted last month on a perjury charge, accused of lying to the grand jury, authorities said.
"We believe that there are people that have information, that knew about what was occurring," Montgomery County, Maryland, Police Chief Tom Manger told reporters at the announcement in the girls' hometown of Wheaton. "That was criminal behavior on their part, not coming forward."
The announcement follows years of torment for the Lyon sisters' family and work by investigators, who had announced Tuesday that a breakthrough in the cold case was coming.
The episode began on March 25, 1975, when Katherine and Sheila walked to the Wheaton Plaza Shopping Center to see an Easter exhibit and grab a slice of pizza.
They were supposed to come home by 4 p.m. When they didn't, their mother called authorities and a major search ensued, according to the Charley Project
, a website that profiles thousands of missing people, mainly from the United States.
Authorities acquired more than 2,000 leads throughout the decades, never leading to any physical evidence.
The most promising lead was a witness in Virginia who reported seeing two girls resembling the victims, bound and gagged in the back of station wagon. Unable to get the entire license plate number, police later deemed the report "questionable."
A convicted sex offender who molested young girls in South Carolina, Delaware and Virginia, Welch was at Wheaton Plaza Shopping Center the same day as the Lyon sisters, investigators say. He told authorities he left the mall with the girls and alleged that he later saw his uncle molesting them. Welch says he never saw the girls again.
The grand jury indicted Welch on Friday after hearing evidence for more than eight months, Brown said. The indictment was unsealed Wednesday.
Manger said the girls' disappearance left a long-lasting mark in the community's collective memory.
"You mention the Lyon sisters' case, people nod their head and say, 'Yes, I remember,' " he said.
Members of the Lyon family attended the announcement.
"If this helps the Lyon family, this is a happy day for me," said Montgomery County state's attorney John McCarthy. "These are wonderful people who have suffered an immeasurable loss."
Authorities are searching for the bodies. Investigators from federal, state and local agencies already have spent "many painstaking hours" in mountainous and snowy terrain, looking for forensic evidence, Brown said. Bedford County is in Virginia's Piedmont region, near the Blue Ridge Mountains.
Krantz told reporters that he will try to extradite Welch to Virginia to face the charges.