WASHINGTON (AP) -- 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.

Yet so far, police hunt in vain.

For two weeks he was 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.

For all that, investigators emphasized yesterday that 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.