Authorities announced the indictment of Lloyd Welch in the murder of the Lyon sisters who disappeared 40 years ago. Here's how the alleged killer spent the last four decades. (The Washington Post)

Lloyd Lee Welch, the 58-year-old former carnival worker charged with murder in the 1975 disappearance of two young Maryland sisters, has told investigators that the girls were abducted so they could be sexually assaulted, law officials said Thursday.

The officials vowed to continue pressing their case, saying that they believe more people were involved, and they spoke about why those responsible 40 years ago killed 12-year-old Sheila and 10-year-old Katherine Lyon. “They were killed in order for their captors to escape detection,” said Bedford County Sheriff Mike Brown.

Speaking at a news conference, Brown and others identified Welch’s uncle, Richard Welch, 70, of Hyattsville, Md., as a target of the investigation. He was first named a “person of interest” in October and has not been charged. He has not commented, but his daughter has said he is innocent.

“He remains and will be a primary focus as we move forward, now that Lloyd Welch has been charged,” said Randy Krantz, the top prosecutor in Bedford.

“We believe that the purpose of this abduction and ultimate murder of the Lyon sisters was for sexual exploitation purposes,” Krantz said.

Lloyd Lee Welch (Delaware Department of Corrections)

Officials also discussed the coming steps and challenges in their prosecution of Lloyd Welch, who faces two counts of first-degree murder. Authorities allege that in March 1975, Lloyd Welch, perhaps with help from others, kidnapped the sisters from a Montgomery County mall where they had gone to look at Easter decorations and visit friends.

It is not clear where the sisters were killed, but authorities have said they suspect that the girls’ bodies were burned or buried on Taylors Mountain, a rugged patch in Bedford County where the Welch family has owned land.

“This is a difficult case,” Montgomery County State’s Attorney John McCarthy said Thursday. “No one could ever look you in the eye and tell you that a case that is 40 years old, in its 41st year of investigation, is not going to be a tough row to hoe.”

Under Virginia law, a murder case can be brought in a place where authorities believe the slaying took place or where a victim’s remains may have been left.

If the case goes to trial, prosecutors are likely to piece together statements from witnesses who saw Lloyd Welch about the time the girls disappeared. They may also rely on statements from Welch himself, who told investigators in recent interviews that he left the Wheaton mall with the sisters and later saw Richard Welch sexually assaulting one of the girls, according to court papers. At one point, court papers said, Lloyd Welch told police that he did not kill the sisters.

According to Brown, the Bedford sheriff, “Lloyd Welch has informed investigators that the Lyon sisters were taken so that they could be sexually exploited by him and Richard Welch.”

Homicide cases without a body are rare but can result in successful prosecutions.

“Without a body, the prosecutor is missing one of the key elements of a murder case, so he’s got an uphill fight proving it in a different way,” said Spotsylvania Commonwealth’s Attorney William F. Neely, who prosecuted a 2004 case in which the body of a child victim was never found.

“The fact that the little girls had never been seen again . . . that’s obviously circumstantial evidence that something bad happened,” he said.

According to police affidavits, Lloyd Welch showed up on Taylors Mountain in 1975 with two red-stained duffel bags that had a strong odor of decay. A cousin, Henry Parker, said in an interview Wednesday that he helped carry the bags and threw them onto a fire.

Another cousin, Connie Akers, told investigators that Lloyd Welch arrived with a duffel bag that appeared to contain bloody clothing and that he asked her to wash the clothes, which she refused to do, according to search warrant affidavits.

Investigators have searched possible crime scenes, including the basement of a Hyattsville home where Lloyd Welch was staying, if briefly, at the time the girls were abducted. It was not clear what, if any, evidence was uncovered.

Virginia defense lawyer Frank Salvato, who had a client convicted in a case without a victim’s body, said prosecutors are likely to focus on Lloyd Welch’s statements and on the terrible nature of the crime, not on where the girls may have been slain.

“If a jury in Bedford County becomes convinced something horrible happened to these two young girls, then the prosecution has cleared its most significant hurdle,” Salvato said.

By the nature of the way Lloyd Welch was charged, it appears that prosecutors do not have to show that he committed the killings. Krantz, the Bedford prosecutor, put it this way at Thursday’s news conference: “A person who commits a felony, such as abduction, and during the course of that abduction, participates in, aids or abets, or by the very nature of them being involved in the abduction, can be held culpable if a death or deaths result from that.”

Carter Garrett, an attorney for Richard Welch, noted that it has been more than eight months since authorities labeled his client as a “person of interest,” yet he hasn’t been charged. Any incriminating material against Richard Welch appears to be coming from Lloyd Welch, Garrett said.

“At this point, it begins to appear to me that Lloyd Welch is lying — just like my client has always said he is lying,” Garrett said. “If they could get anything to hang their hat on, I believe my client would be under indictment.”

In a letter last year to the The Washington Post, Lloyd Welch said he had nothing to do with what happened to the sisters. “They are looking at the wrong person,” he said.

Lloyd Welch, a prison inmate in Delaware, where he was convicted in 1998 of sexually assaulting a 10-year-old girl, is expected to be transported to a jail in the Bedford area within 60 days.

Dana Hedgpeth contributed to this report.