Authorities in Montgomery County, Md., say they have identified and are ready to announce a "person of interest" in the 1975 disappearance of two sisters -- a case that has remained unsolved for nearly four decades.

On the afternoon of March 25, 1975, 12-year-old Sheila Lyon and 10-year-old Katherine Lyon left their home in suburban Washington, D.C., to walk to the nearby Wheaton Plaza shopping center. Investigators say witnesses saw the girls inside the mall before they disappeared. The girls never returned home and no sign of them has ever been found.

Investigators say Lloyd Lee Welch, now 58-years-old, was noticed paying attention to the sisters the afternoon they disappeared, reported. Welch, a convicted sex offender, has been in prison in Delaware since 1997. He worked as a ride operator for a carnival company that often set up at malls. He was arrested in several states and has been charged with sexual offenses against young girls.

Authorities say Welch traveled extensively throughout the United States and investigators will be requesting help from the public in gathering information about this person, his associates, and his activities.

The girls' father, John Lyon, was a well-known Washington radio personality and used his platform to solicit tips and other information about the possible whereabouts of his daughters.

Capt. Marcus Jones, the commander of the Montgomery County Police Department's major crimes division, called the identification of the person of interest "the biggest break we’ve had in quite some time" in the case in an interview with The Washington Post. 

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