It was one of those cases that haunts a community. Two sisters vanished while walking home from a mall in a quiet suburb of Washington, and a widespread search yielded nothing. As months turned to years, and then decades, hopes of learning what happened to the girls dwindled.

But the case of the sisters, Sheila and Katherine Lyon, snapped back into focus Wednesday, more than 40 years after they disappeared from a street in Wheaton, Md., as law enforcement officials said that a man had been charged with their murders.

With the girls’ parents standing silently to one side, officials announced the indictment of Lloyd Michael Welch Jr., 58, at a news conference in Wheaton, near the girls’ childhood home. Katherine, 10, and Sheila, 12, were killed in rural Bedford County, Va., about 200 miles away from where they were abducted, investigators say. But despite extensive searching through that wooded region, the girls’ bodies have never been found.

Image Lloyd Michael Welch Jr. in a 1977 mugshot from when he was arrested on charges of residential burglary near Wheaton Plaza. Mr. Welch was charged with the Lyon sisters' murders on Wednesday. Credit... Montgomery County Police Department

Mr. Welch, an imprisoned child molester, was charged after an investigation that officials said was slowed by obstruction by members of his family. The officials repeatedly stressed that the inquiry remained open, suggesting that Mr. Welch did not act alone.