R By Shannon McCaffrey, Seth Borenstein and Tony Pugh

OCKVILLE, Md. (KRT) – A bus driver was shot and killed Tuesday in what appeared to be the 10th slaying by a Washington-area sniper, and authorities revealed the chilling partial contents of a note the sniper left them over the weekend: “Your children are not safe anywhere at anytime.”

Montgomery County, Md., Police Chief Charles Moose said authorities had been contacted again Tuesday by a man they think is the shooter, continuing the high-stakes dialogue that is being conducted in part through the media.

“We will be responding soon,” Moose said.

The threat against children was added as a postscript in a letter left Saturday near a steakhouse in Ashland, Va., where the gunman wounded a Florida man. In the note, the sniper reportedly sought money.

Richmond, Va., area officials shut down schools Monday and Tuesday in response to the note. In Montgomery County, where students have been kept inside and the schools locked down since Oct. 3, schools remained open Tuesday and plans for Wednesday were up in the air. School authorities advised parents to watch late newscasts Tuesday or consult the schools’ Web site for updates.

Early Tuesday morning, Conrad Johnson, 35 and a father of two, was gunned down on the top step of a commuter bus in Aspen Hill, Md. If the killing is connected to the sniper, it will mark the shooter’s return to Montgomery County, where the rampage began and where the death toll already stands at five.

Johnson was shot just two long blocks from the Michael’s craft store where gunfire shattered a window Oct. 2. Patrons were unharmed. Ballistics evidence from the store matched the gun subsequently used by the sniper, who has since shot 12 people. Three of his victims were wounded, including a 13-year-old boy who was on his way to school in Bowie, Md.

After Tuesday morning’s shooting, police swung into action, clamping roadblocks on some of the main traffic arteries in the Washington region as the morning commute was getting under way. Traffic was snarled for miles until roadblocks were lifted midmorning.

Police cast an even wider net Tuesday than they had before, pulling over male drivers in all sorts of vehicles instead of focusing on the white vans and box trucks that witnesses at earlier shootings had described and on which authorities had concentrated.

“The dragnet is a long shot,” said Joseph McNamara, a former San Jose, Calif., police chief and FBI consultant. McNamara said such a technique was most successful when authorities had a particular license plate number, vehicle or suspect description to narrow their search.

Moose said the latest shooting had yielded no “vehicle lookout to share. No person lookout to share,” meaning no enhanced description of the sniper or his vehicle.

“We’re doing everything in our power to keep people safe,” the police chief said.

Stunned family and friends mourned Johnson on Tuesday.

Some 30 relatives, some visibly upset, swarmed to Suburban Hospital in Bethesda, Md., where Johnson was taken by helicopter. Through a hospital spokesman they declined to comment.

Neighbors in Johnson’s cul de sac in Oxon Hill, Md., recalled the burly 6-foot-2-inch sports fan playing touch football outside with his two sons, one age 7 and the other in his early teens.

Steve Addison, who used to wash his car with Johnson, described him as ” a real family man.”

Addison said, “He loved his boys, always taking care of them.”

Originally from the West Indies, Johnson was also known as something of a block leader and neatness freak, taking it upon himself to make sure neighbors didn’t play their music too loud or let their modest yards become messy.

“He always was laughing and joking with you,” said neighbor James Campbell.

A blue home-security sign was perched outside Johnson’s tidy cream-colored townhouse.

At Montgomery County’s commuter-bus headquarters, drivers took up a collection for Johnson’s family. Some were visibly shaken.

“We take this personally,” driver Greg Carrington said. “We’re a family.”

Some drivers, who like Johnson must operate in the open, were fearful.

“You’re pretty much a target. You’re in harm’s way. There’s nothing we can do. We don’t have bulletproof glass,” driver Garfield Hardy said.

Johnson was preparing for his morning route when he was shot.

The site is bordered by an apartment complex, where some witnesses heard a single gunshot, and a wooded park. It is not near any interstates but is close to several busy multilane roads that funnel commuter traffic in and out of Washington.

The mood has been jittery in Montgomery County since the sniper attacks began, but nerves ratcheted up again Tuesday after the first attack there since Oct. 3.

“It’s kind of unsettling now that all this is going on in Maryland again,” said Laura Roberts, a PTA president in the nearby Montgomery County town of Kensington. “It’s always more nerve-racking when it’s in your back yard.”

The shooter killed five people in Montgomery County on Oct. 2-3.

The county recorded only six murders in 2001, according to police department data.