Lloyd Lee Welch
Lloyd Lee Welch is pictured in this 1977 booking photo courtesy of the Montgomery County Police. Welch, who has been imprisoned since 1997 as a "convicted child sex offender" was named a "person of interest" in the 1975 case of the disappearance of two sisters last seen at a Maryland mall by Chief Tom Manger of the Montgomery County Police Department during a press conference February 11, 2014.REUTERS/Montgomery County Police/Handout via Reuters

An imprisoned sex offender was charged with first-degree murder of two Maryland sisters, who disappeared from a suburban Maryland mall in 1975, authorities announced on 15 July.

According to Fox News, 12-year-old Sheila Lyon and her 10-year-old sister Katharine walked from their home to the Wheaton Plaza Mall in March 1975, but never returned home. The girl's remains were never found.

The case, which has remained a mystery for decades, finally led investigators to a suspect. Fifty-eight-year-old Lloyd Lee Michael Welch Jr, a child sex offender who is serving a long prison sentence in Delaware, was indicted on two first-degree murder charges by a grand jury on 10 July. Welch also faces charges of abduction and murder with the intent to defile.

In a press conference on 15 July, Montgomery County Attorney John McCarthy said, "This case has never left the collective consciousness of this police department nor our community."

McCarthy continued, "We know what Katherine and Sheila were like....These were wonderful, wonderful, naive, young children...It has remained with us forever."

Fox News reported that at the time of the sisters's disappearance, a then 18-year-old Welch was a carnival worker and drifter. According to investigators, Welch was at the mall the day the girls went to the mall and was witnessed paying attention to them.

In 2014, authorities reignited the search for the girls's remains in the mountains of Bedford County, Virginia, some 200 miles from Wheaton.

Welch and his 70-year-old uncle Richard Welch had previously been named persons of interest in the case. According to Fox News, Richard Welch's wife Patricia was charged with perjury in December after testifying to the grand jury.

The Washington Post reported that Lloyd Welch denied his involvement in the girl's disappearance in a letter. Police affidavits however, revealed that Welch told investigators he took the girls from the mall and witnessed one of them get sexually assaulted by his uncle. He alleged he left the home and never saw the Lyon sisters again.

Welch allegedly asked a relative in rural Virginia to wash bloody clothes he carried in a duffel bag, which investigators believe could link him to the sister's presumed deaths, the Post reported.