A SERIAL killer unlike any other in history has single-handedly brought America to its knees. In 22 days the sniper has killed 10 people, critically injuring three more, bringing the terrified Washington district to an almost grinding halt. BEVERLY GREENBERG examines how the killer's mind could be working and what the devastating effects of his actions have been

WHO knows what can be going through the mind of the deranged sniper who has single-handedly paralysed America in a vice-like grip of fear.

This is a man whose cold-blooded, random method of killing has not only terrified Americans in the Washington district into staying indoors, but who has frightened an entire watching world into wondering if his brand of terror is a horrifying vision of the future.

America, the world's richest, most powerful nation, is on its knees. Families in its capital are terrified prisoners in their own homes, children are being kept off school, women are shopping online, and the everday sound of laughter as youngsters play outdoors has been replaced by an eerie, subdued silence.

Cars are running out of fuel because drivers are too frightened to stop for petrol -- two of the attacks have taken place at service stations -- while those who do venture out to shopping malls run in zig-zags from their parking spaces. They would look ludicrous in any other circumstance.

On Tuesday, the serial sniper claimed his 13th victim, a bus driver who died after he was shot in the chest. The death toll is now 10 -- with a further three victims seriously injured. All this devastation and terror has been caused within 22 days.

The warning issued to Washington's police in a note left at the scene of one of the shootings was chilling, evil and left no room for misinterpretation -- "Your children are not safe, anywhere at any time."

This is a killer with no apparent motive. He kills indiscriminately and with a frightening ruthlessness. Children, women and men -- all have been his victims.

Criminal experts now fear that the sniper is not only enjoying the terror he is inflicting, but relishing the hunt for him.

W Scott Thornsley, a criminal justice professor at Mansfield University in Pennsylvania, specialises in serial murderers. He said: "This is a huge game to him, and he has succeeded beyond his wildest expectations. The pleasure for him now is in not getting caught, even when he leaves clues. He seems to be enjoying the hunt and the escape as much as the killing."

This killer also differs from the usual serial murderer in the manner in which he strikes. Most get a thrill in the killing. Experts have revealed that many enjoy killing with a hands on approach -- using their hands, a knife or a rope -- and feel most gratification in watching their victims' terror, knowing they have the power to take their last breath.

But the sniper is killing from a distance. The closest he has come to one of them is 100 feet, leading some experts to suggest the thrill comes not from watching his victims fall, but with the next headline. The single shots come from out of nowhere, the unsuspecting victims do not fall into any single category and there appears no motive. In short, all the usual avenues of investigation do not exist.

In desperation, police have caused traffic mayhem in organising five giant road blocks within 14 days. But the area's maze of side streets have beaten police, who have emerged empty-handed each time.

Now, police chief Charles Moose is appealing for the killer to resume contact. In a vast country in which guns are easily available, it could be detectives' best chance of a result.

Could this sniper set a new evil trend? If a similar character had appeared in a film, audiences would have found it far-fetched. But this is now a reality. There is a person out there so cold-blooded that his choice of victim is irrelevant. Snuffing out a stranger's life means nothing to him.

What turns a person into such a ruthless killing machine? How has society managed to create such a monster? And could the terror gripping America be replicated in any town or city throughout the world?

This is an anonymous killer whose method of murder could leave every one of us at risk.

The rest of the world holds it breath as Washington's residents continue to look over their shoulder in fear.