ROCKVILLE, Md. --

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Before Tuesday, Montgomery County, Md., Police Chief Charles Moose urged people to carry on with their routines despite the sniper attacks, but that has now changed.

Tuesday Moose said, "Your children are not safe, anywhere at any time," quoting a note apparently written by the sniper as part of an increasingly public dialogue with a man suspected of killing at least nine people and wounding three.

The words were reportedly left at the scene of Saturday night's shooting in Ashland, Va. Moose, leader of the multi-agency task force investigating the shootings, repeated them 11 hours after bus driver Conrad E. Johnson, 35, was shot to death in Aspen Hill, Md., while preparing to begin his morning route.

Authorities suspect Johnson is the sniper's 13th victim. They are awaiting ballistics tests to confirm those fears. The federal Bureau of Alcohol, Tobacco and Firearms is examining the bullet at its lab in Rockville, Md.

Moose also issued a plea to the killer, urging him to continue a dialogue that began after Saturday's shooting. "It is important that we do this without anyone else getting hurt," Moose told reporters Tuesday evening in comments directed at the sniper.

Authorities received the latest message from a person they believe to be the killer after Tuesday's shooting, a source familiar with the case told The Associated Press. The Baltimore Sun, citing unidentified sources, reported that a letter left Tuesday at a park near the shooting repeated demands first made in Saturday's note.

The Associated Press also reported that a senior law enforcement official, who spoke on condition of anonymity, said Saturday's note demanded $10 million. "We have researched the options you stated and found that it is not possible electronically to comply in the manner that you requested," Moose said in a message that authorities said would be understood by the sniper. "However, we remain open and ready to talk to you about the options you have mentioned."

Moose said the sniper was seeking an 800-telephone number to talk with authorities. The chief offered to set up a private post office box "or another secure method" if the killer preferred. "You indicated that this is about more than violence," Moose said. He did not answer reporters' questions about the statement, the longest he has made to the suspect.

In Virginia, more than 140,000 students in the Richmond area were to return to school Wednesday after a two-day school closure prompted by Saturday's shooting. Washington area schools planned to open under the same heightened security measures, including no outdoor activities that they have operated under for more than two weeks.