At a terrible cost, police are learning more about the Washington-area sniper day by day, death by death. Insights into his voice, penmanship, grammar, mood and mode of operation have flowed from his communications, and other evidence is mounting.
Late Wednesday night, the case leaped forward when police announced that an arrest warrant had been issued for an "armed and dangerous" man wanted on weapons charges.
For the first time, a name was linked to the case even as police said it could not be assumed that the man — John Allen Mohammed, also known as John Allen Williams — was involved in the killings.
Police also descended on the back yard of a Tacoma, Wash., home, sifting through dirt and hauling away a tree stump in what a law enforcement official said was a search for ammunition evidence.
"The investigation has taken us down different avenues and roads that we need to explore," said another official, Montgomery County, Md., Police spokeswoman Capt. Nancy C. Demme.
For more than two weeks the killer was an almost complete mystery — a specialist in leaving without a trace beyond a body and bullet fragments, fleeing with his literally smoking gun. Police only seemed to have a vague idea about his vehicle and even that lead weakened as time went on.
Now his temper and tone have been exhibited, thanks to his keen wish to be in touch with police.
Authorities have a voice to analyze and track to its source, some sort of third-party phone number and, conceivably, fingerprint evidence or genetic flotsam from his letters and crime scenes.
Whether his recently disclosed demand for money is a diversion or the point of the assaults that have left 10 people dead, three wounded and parents fearful that he's after their children, it provides yet another way to hunt a killer that was missing until he opened lines of communication with police. Authorities have not ruled out more than one shooter.
For all that, investigators emphasized no single lead is a magic pill in this case.
"Just like an illness, some things don't respond to treatment right away," said Mike Bouchard, special agent with the federal Bureau of Alcohol, Tobacco and Firearms. "Some cases don't respond to our methods right away."
He said: "We get one step closer every day."
Criminologist W. Scott Thornsley says the sniper's communiques — only snippets of which have been made public — are a compulsive signature of sorts, and a potentially valuable clue that places the killer in greater danger of getting caught.
Thornsley, who teaches about serial killers at Mansfield University in Pennsylvania, said the sniper appears so addicted to the attention he is getting that he is trying sensational ways of maintaining notoriety beyond the rising number of victims — intentionally dropping clues, threatening children and bidding for a $10 million payoff.
Steven A. Egger, a former homicide detective who directed New York State's pioneering computer system for tracking serial killers, said no one outside the investigation can know how useful the physical evidence might be. He predicted the sniper will be caught by a fluke, by painstaking police work or a combination.
"This person could be masking his voice," said Egger, who teaches criminology at the University of Houston at Clear Lake. "He could be writing in different ways than he normally writes."
Yet even a distorted voice or writing style is more than investigators trained in language patterns, prose and deceptive communication techniques had before.
Among the possibilities for investigators:
— That experts can find meaning in the sniper's writing style and bad spelling, which they have not shared publicly.
Soon after the disclosure that the writer wrote awkwardly, police appealed to immigrants to come forward if they know anything. Illegal immigrants are often too worried about their status to tell police what they know about a crime.
Police insisted they did not make this appeal because they think the sniper is foreign-born; indeed, he would not be the first domestic serial killer with awful grammar.
Communiques made public have helped before. The Unabomber was caught when his manifesto was published and his brother, recognizing his sibling's ranting style, tipped police.
— That his notes might yield fibers, DNA, fingerprints or distinctive ink or paper that can be traced.
— That his voice, even if disguised, might betray a local, regional or foreign accent and be recognizable to those who know him — although the public has not heard it.
He is thought to have spoken several times with police or at least left voice messages for them. In addition, according to published reports, a man now believed to be the sniper made agitated phone calls to the public hot line — and got the brush-off from a disbelieving trainee when he managed to get through.
— That his request for a special toll-free number to speak with police and the options he has apparently outlined for receiving a payoff will tip police to his location. They traced one call to a Richmond, Va., pay phone but arrested the wrong people.
The sniper's first known communication was a tarot death card on which he wrote, "I am God," left behind after the Oct. 7 wounding of a 13-year-old Maryland boy.
A longer and more telling note was left after the wounding Saturday night of a man outside an Ashland, Va., steakhouse. The letter demanded cash, warned everyone that "your children are not safe," and opened the halting, extraordinary dialogue with police.