MANASSAS, Va. -- Perhaps the biggest mystery remaining before trial begins Tuesday for sniper suspect John Allen Muhammad is the true nature of his relationship with his teenage companion, fellow suspect Lee Boyd Malvo.

The men's relationship has become a key and complex element in each case, with all sides painting different portraits of the dynamic.

Muhammad's defense team has said evidence points toward the young suspect as the triggerman. Malvo's attorneys now say the older man was so domineering that they are basing an insanity defense on the argument that the teen was indoctrinated to the point he could no longer tell right from wrong.

Malvo's prosecutors portray it differently, saying the teen laughed about the shootings that induced a wave of fear in the Washington, D.C., region during a three-week spree last October, and admitted pulling the trigger in several shootings.

At a hearing earlier this month, Malvo took the Fifth Amendment when he was asked about his relationship with Muhammad.

Muhammad's defense team has revealed little about how they will fend off prosecutors' claims that Muhammad served as captain of a two-man "killing team."

They could blame Malvo outright, or they could simply argue that prosecutors don't have the evidence to convict their client, without ever pointing the finger at Malvo.

Complex relationship

Robert Cleary, a former U.S. attorney who prosecuted Unabomber Theodore Kaczynski, said he suspects Muhammad's defense will explicitly blame Malvo.

If the case against Malvo is strong, Muhammad's defense "is almost compelled to point the finger at Malvo," Cleary said.

Malvo, 18, and Muhammad, 42, are charged with 13 shootings, including 10 deaths, in Maryland, Virginia, and Washington, D.C. They are suspected or charged with shootings in Georgia, Alabama, Louisiana, Arizona and Washington state.

A legal brief filed in February in the Malvo case was the first public document to describe the unusual relationship between the men.

Deputy Commonwealth's At-torney Raymond Morrogh said in the brief that while they allegedly acted as equals in the shootings, Malvo referred to Muhammad as his father. They are not related.

Malvo first met Muhammad in 1998, when he and his mother moved from Jamaica to Antigua. Muhammad, U.S. Army veteran and mechanic, allegedly supplied Antiguan passports to people looking to emigrate illegally to the United States, including Malvo and his mother. Malvo ran away from his mother in Florida in October 2001 to join Muhammad in Bellingham, Wash.

Prosecutors and legal experts also warn that the relationship gives rise to unique challenges in the cases.

"The public has a very strong view of how this case should turn out, but they don't necessarily have an appreciation of the complex legal and evidentiary decisions a judge has to make," said James Willett, one of three prosecutors in the Muhammad case.

Prosecutors will try to pull off a rare feat in Muhammad's trial: obtaining a death penalty in a shooting death for a defendant who didn't pull the trigger.

Death penalty for triggerman

Muhammad faces two capital counts for the sniper shooting of Dean Harold Meyers, 53, of Gaithersburg, Md., while he pumped gas near Manassas on Oct 9, 2002.

One charge is the first prosecution under an anti-terrorism law passed by Virginia after the Sept. 11, 2001, attacks. The state will have to show not only that Muhammad participated in a murder, but that the intent was to influence the government or to intimidate the civilian population.

Defense lawyers argue that Muhammad can only get the death penalty if he was a triggerman in the killings, while prosecutors say recent case law shows they need only prove Muhammad was the "instigator and moving spirit."

The two charges raise questions for prosecutors about how to put on their case, said Cleary.

For instance, one piece of evidence could bolster the case that Muhammad and Malvo were a team participating in acts of terrorism, but that same evidence might weaken the argument that Muhammad was an instigator of the shootings.

Also, the simple fact that two defendants, in separate trials, have the option to blame the other complicates matters for prosecutors, Cleary said.

For Malvo, whose trial for a Fairfax County killing was moved 200 miles to Chesapeake, the direct evidence is more compelling. Malvo's fingerprints were on the Bushmaster rifle used during the sniper spree, and Malvo has confessed to several of the killings in interviews with police and in conversations with jail guards after his arrest.

Much of the evidence Malvo's lawyers plan to introduce about indoctrination to bolster their insanity defense will also be useful at sentencing, experts say.

"The big push is going to be convincing a jury that they shouldn't receive the death penalty," said Joseph Bowman, a former defense lawyer who has handled several death-penalty cases in Virginia, which executes more killers than any other state except Texas.

"They can say he was just a kid, that he was greatly influenced by Muhammad."

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On the Net:

Muhammad case: www.pwcgov.com/ccourt/special

Malvo case: http://www.fairfaxcounty.gov/courts/cases/malvocase.htm