to feed her own children.

It is possible that Muhammad chose Washington for his killing spree because it is the seat of a national government against which he wished to strike.

It is also possible that he simply chose it because of convenience. He and his stepson have reportedly resided in the Washington suburb of Clinton, Md., off and on since as early as 1999.

One thing is sure: as a case of mass murder, the Washington snipers shootings fit no previous pattern of American crime.

From the age and race of the killers, to the timing, location, and possible motives of their acts, many aspects of the murders were unprecedented, say experts.

"This whole case has been very erratic from the beginning," says Tomas Guillen, a professor at the University of Seattlerobbery in Montgomery, Alabama, which provided a crucial fingerprint, which led them to the teen Malvo, and thence to his stepfather.

Brian Levin, director of the Center for Hate and Extremism at California State University at San Bernardino, says he doesn't believe that these suspects wanted to get caught. The clues that were left were part of the sniper's sociopathic desire to prove he was smarter than everyone else, he explains.

"I honestly think it was his way of saying, 'OK, I'll throw you a slow pitch and you'll still strike out.' It was part of his thing with power and control and authority. He was saying to the police, 'I'll give you a clue and you'll still miss it.' But they didn't."

Professor Levin says ego will often trip up