Sniper holds America to ransom with warning: Your children aren't safe anywhere, at any time

A chilling "ransom note" from the Washington sniper which threatened children and demanded the payment of $10m was revealed yesterday after the gunman apparently struck again, killing a Maryland bus driver.

Police said they had received a message from the sniper which read: "Your children are not safe anywhere at any time."

The message was the postcript to a three-page letter found at the scene of a shooting last Saturday.

Late last night, Charles Moose, the Montgomery County Police Chief, suggested authorities had been in repeated contact with the sniper.

"We have researched the options you stated and found that it is not possible electronically to comply in the manner that you requested," Mr Moose said. "However, we remain open and ready to talk to you about the options you have mentioned."

He said the sniper was seeking a toll-free telephone number to talk with authorities, and offered to set up a private post office box "or another secure method."

"You indicated that this is about more than violence. We are waiting to hear from you."

The revelation of the threat against children came after the sniper apparently struck again, claiming his 13th victim and 10th fatality.

Conrad Johnson, 35, who was married and the father of two children, was fatally wounded by a single shot as he prepared to start his early morning bus route, no more than a mile from the scene of the first of the series of shootings almost three weeks ago.

Though police could not immediately confirm the killing was the work of the sniper, the incident appeared to bear many similarities to previous shootings and officers said they were treating Mr Johnson as the gunman's latest victim. The results of ballistic tests are expected later today.

Mr Moose said: "The person or the people involved in this have shown a clear willingness and ability to kill people of all ages, all races, all genders, all professions, different times, different days and different locations."

Mr Johnson was shot shortly before 6am as he stood on the top step of his bus while it was parked in a quiet road in Aspen Hill, Maryland, about 10 miles north of Washington, and close to several of the gunman's previous attacks.

The driver had been finishing paper-work and cleaning out his vehicle when he was struck in the stomach by a single bullet ­ possibly fired from a small wooded park situated about 50 yards from the bus.

Mr Johnson was taken to a hospital in the nearby Washington suburb of Bethesda where he underwent emergency surgery to repair extensive damage but he died less than five hours after he was shot.

Douglas Duncan, a Montgomery County executive, said Mr Johnson had been a bus driver for 10 years. "He loved basketball, he loved his kids, [he had a] very large extended family," he said. "He is going to be missed greatly."

As police with bloodhounds continued to search a wooded area opposite where Mr Johnson's bus had been parked, Chief Moose revealed the content of a letter found close to the scene of the gunman's previous attack.

This took place on Saturday night outside a restaurant near Richmond, Virginia. After the shooting police received a telephone call which led them to a wooded area near the restaurant where they found the three-page letter.

Mr Moose said he was revealing the exact wording of a segment of the letter, following reports that it referred to the safety of children.

Those details had previously been made available to schools authorities in the Richmond area, leading them to keep many of the region's schools shut yesterday. "We recognise the concerns of the community and therefore are going to provide the exact language that pertains to the threat," he said. He declined to reveal the content of the whole letter because he said it would impede the investigation.

After yesterday's shooting police immediately set up roadblocks, creating chaos on many of the area's major roads but not trapping the gunman.

With panic increasing every day it was reported yesterday that federal authorities are considering taking over the investigation.

It has become clear that the gunman has had at least two ­ and possibly three ­ telephone conversations with the authorities. It appears that some of those conversations were unclear, leading police to appeal to the sniper earlier this week to get back in touch with them.