McLEAN, Va. - It galled her to do it, but Sarah Dillon was desperate for answers, so she wrote letters to convicted snipers John Allen Muhammad (news) and Lee Boyd Malvo (news) : If you murdered my son, please confess, she wrote.

She got no reply.

"I've been waiting for answers for seven years," said Dillon, who took to wearing a button that said "Billy Gene Dillon is a very important person" as a reminder that his killing remains unsolved.

Sarah Dillon is not the only person with unanswered questions about the killing spree initiated by Muhammad and Malvo seven years ago, which culminated with 13 shootings and 10 deaths over a three-week span that terrorized the Washington region.

As Virginia prepares to execute Muhammad on Tuesday, authorities are unable to answer perhaps the most basic question about the killings: How many people did he and Malvo shoot and kill?

The killing spree in the Washington area in October 2002 is well documented. Beginning on Oct. 2, Muhammad and Malvo shot 13 people at random with a high-powered rifle, firing from the trunk of a modified, beat-up Chevy Caprice. Ten were killed before authorities finally tracked down the pair at a Maryland rest stop.

But the sniper shootings started before Muhammad and Malvo reached the Beltway, with a number of victims killed or wounded as
the duo drove across the country.

Investigators have clearly linked them to some of these prelude shootings, though they have never stood trial for them. Others fall
into a gray area - police have suspicions, perhaps, but no proof. 

The question became even murkier in 2006, when Malvo reportedly confessed to four additional shootings, including two killings,
that had not been linked to him.

If Malvo's reported confessions are accepted as true, it would mean he and Muhammad are responsible for 27 shootings resulting in 17 deaths in 10 states (Maryland, Virginia, Alabama, Washington, Georgia, Texas, California, Florida, Arizona and Louisiana) plus the District of Columbia.

But Malvo would only talk to police in jurisdictions that promised not to prosecute him, a deal some agencies weren't willing to make.

So in Clearwater, Fla., the golf course shooting of Albert Michalczyk on May 18, 2002, officially remains unsolved, though Michalczyk took Malvo's reported confession in 2006 as confirmation of something he long suspected.

"My wife immediately thought it was these guys," Michalczyk said at the time. "We put two and two together, but we never came
up with four. Now, we are coming up with four."

Police from Tucson, Ariz., consider the golf course killing of Jerry Taylor solved based on their interview with Malvo, which they
obtained only after agreeing not to prosecute him.

The victim's daughter, Cheryll Witz, decided that knowing the truth was more important than seeing Malvo face criminal charges,
given the fact that he was already serving life in prison. At one point, Malvo even called Witz on the telephone and apologized. 

Back in Texas though, Sarah Dillon still doesn't know who shot and killed her son, Billy Gene Dillon, 37, in May 2002 outside a
rural Denton County home about 40 miles north of Dallas. Local authorities submitted bullet fragments in 2002 from their investigation of Dillon's death to the task force that investigated the sniper shootings, but tests were inconclusive.

At the time, they had little reason to suspect the snipers except for the fact that Dillon had apparently been shot at a distance by a high-powered rifle, just like the victims of the D.C.sniper spree. Police agencies from across the country took similar
actions, to see if unsolved killings could be connected to Muhammad and Malvo.

Denton County sheriff's spokesman Tom Reedy expressed some frustration about the inability to get answers from the Washington-area authorities regarding Billy Gene Dillon's death.

"If they give you an answer, let us know," he said.

The FBI (web) , part of the sniper task force that helped eventually catch Muhammad and Malvo, declined to comment on how many people
the snipers shot and killed, except to say the question is "complicated."

"To further complicate it, the statements of Muhammad and Malvo need to be relied on as to who performed any given shooting.
Needless to say, their statements cannot be vetted for each and every event," FBI spokesman Richard Wolf said in an e-mail.

State and local authorities, including Fairfax County (web | news) Police, Montgomery County (web | news) Police, the Montgomery County State's Attorney
and Maryland Office of the Attorney General all referred the question to other agencies.

The prosecutor who put Muhammad on death row, Prince William Commonwealth's Attorney Paul Ebert, said it may be impossible to know how many people were killed.

"I don't know that you can trust anything Malvo says," Ebert said, referring to Malvo's reported confessions. Malvo's statements
have not always been consistent - he at first took responsibility for pulling the trigger on all the shootings, but later testified that Muhammad, more often than not, was the shooter.

"There may well be more we don't know about, but who knows?" Ebert said.

Carmeta Albarus Lindo, a social worker who testified on Malvo's behalf at his first trial and has maintained a relationship with
him, said it's up to Malvo's attorneys to decide whether he will provide statements to police without promises of immunity. Malvo's attorney on the Maryland cases, William Brennan, said he can't comment because Malvo could still theoretically face
prosecution in other states.

Sarah Dillon, meanwhile, is well aware that Muhammad's death eliminates one of the people who can answer her questions about her son's murder.

"All I'm asking for is answers," she said, "before they leave this world."

 Email To Friend