A woman loading shopping into the back of her car has become the 11th victim of a sniper terrorising the area around the American capital. Nick Morrison asks: what sort of man carries out such an apparently random, cold-blooded crime?

FOUR were at gas stations, three filling up with petrol and a fourth using the forecourt vacuum. Another three were in shopping centre car parks. One was cutting the grass at a car showroom. One was sitting on a park bench, another standing on a street corner and the youngest, a 13-year old boy, was being dropped off at school.

Seven have been male, four female, and of those identified, four were white, three black, one Hispanic and one from the Indian sub-continent.

It seems the only link between them is that they have all fallen victim to the man who has brought fear to the streets of the capital city of the most powerful nation on Earth.

Ever since the windows of a craft store in Aspen Hill, Montgomery County, Maryland, were shattered on Wednesday, October 2, the sniper has coolly, methodically, and apparently randomly, picked out his victims.

The shooting of a woman in Falls Church, Virginia, on Monday night, brought the number of victims to 11. Nine of those were killed, each with a single bullet. Two have been injured, including the 13-year-old boy.

The killings have brought a state of paralysed fear to Washington DC and the surrounding counties, but with no idea where the sniper will strike next, there is no refuge in knowing which places should be avoided.

All of the victims have been shot with a .223 calibre bullet, fired at long range, but the only other clues appear to the sighting of a cream or white van near the scene of some of the shootings, and a tarot card found beside a spent bullet casing, inscribed with the message: "Dear policeman: I am God." The police, with nothing to link the killings other than the identity of the killer, seem baffled.

While investigators have few leads, the sniper displays all the characteristics of a classic psychopath, according to Cary Cooper, professor of psychology at the University of Manchester Institute of Science and Technology (UMIST).

'He is probably psychopathic, in the sense that he has no conscience about what he is doing or who he is killing, whether it is women or men," he says. "He is also at a fair distance from them, so in a way he is not actually seeing what he is doing."

Prof Cooper says the sniper's skill with a weapon - using only one bullet in each of the shootings - suggests he may have a military background, or may have been a member of a gun club or a policeman. But there are very few clues as to why he has embarked on such an apparently random killing spree.

"There will be something that has motivated him, but we won't know what it is until we see what kind of person he is," he says.

"He is obviously angry at something or somebody, although I don't know who that is. He may have been thrown out of the military, or of a gun club, or he may have been rejected when he tried to join the police."

Although the sniper is thought to have an accomplice - a woman has been seen at the wheel of the van - Prof Cooper says the killer is likely to be a loner, not linked to anyone who is leading another, normal, kind of life.

"There will not be anybody saying 'All this time, I never knew'," he says.

Even though the killings seem chillingly methodical, there may be similarities between other mass-murderers, according to Gerard Bailes, consultant in the forensic psychology service of East Anglia.

He says both Michael Ryan and Thomas Hamilton, responsible for the Hungerford and Dunblane massacres respectively, planned their crimes carefully, even though they seemed to be carried out in a frenzy, rather than the deliberate manner of the Washington sniper.

"Both Ryan and Hamilton practised beforehand, and a tremendous amount of planning went in to what they did. Hamilton took a number of guns with him in case some jammed, and put coloured tape on them so they could be easily distinguished," he says.

"This sniper is finding a location safe from prying eyes, and although there may be an opportunistic element, there has to be a certain amount of advance planning."

But it is a mistake to see the killings as motiveless, he says, even though the motive may make no sense to the rest of us.

"People say 'How can somebody do that?' but that is to look at it from their perspective. It may appear to be senseless, but you have to look at the motivation, and look at what purpose it serves," he says.

"It can be about control, power, the thrill and excitement of killing. It may be about vengeance, they may have delusions of grandeur or it may be symbolic. We don't know anything about this person's background, but there is a reason why people do the things they do."

For Prof Cooper, one possible explanation for the killings is simply in showing how much smarter the sniper is than the police. This may back up the theory that he has a grudge against the police, and explains the message on the tarot card.

"I don't know what he is trying to prove, other than trying to outsmart the police. He obviously has total disregard for the police and authority, and he is trying to demonstrate their incompetence," he says.

"I think it is him against the police. It is not about the people he is killing - he is not interested in them - he is interested in showing the police up, which makes me wonder whether he might be an ex-policeman or he has been rejected from the police force.

"He is really humiliating the police, and showing how clever he is, because there is no way to track him."

Just because the killings seem to be carried out so methodically, it does not mean the sniper is not motivated by anger, but in his case it is a controlled anger, says Prof Cooper. He is exhibiting the lack of emotion of a psychopath impervious to the feelings of others.

And the panicked response to his random attacks may fuel the desires which brought him to launch his killing spree.

"It makes him feel powerful. He now has the whole area frightened of him, and that is giving him a sense of power and influence, that maybe he doesn't have in his ordinary life.

'People are terrified. They are putting their petrol in and then jumping inside their cars. People are not going shopping because of this. To a distorted mind, this means 'Look how powerful I am. I have the capital of the United States frightened to death of me'."

Chillingly, Prof Cooper suggests this means the sniper will not stop until he is caught. "He will carry on until he is stopped. He is not going to stop. If the objective is to show the power and influence he has, and that he can have a whole community living in fear, then there is no reason to stop. The only reason he might stop is if he moved away, and then he'll do it somewhere else."

But Prof Cooper says there may be a glimmer of hope for those detectives who have so far found themselves several steps behind the sniper.

"He will slip up, and they will find him. It may be because he wants people to know. It is alright for him to feel powerful and influential, but he may want other people to know who he is, and that could be his downfall."