It is just over three years since the self-styled Mardi Gra bomber began his bizarre campaign. He marked the anniversary by leaving an explosive device in a carrier bag outside the West Ealing branch of Sainsbury in London last weekend.
Sainsbury, which has been targeted six times in the past month, has stepped up security at all its supermarkets. The fear is that Mardi Gra - who police are certain is a man, acting alone - may be planning something spectacular during the shopping rush in the run-up to Christmas.
The detectives on the case, from Scotland Yard's Organised Crime Group, know a great deal about his methods. His home-made bombs - 30 so far - are painstakingly built from shotgun cartridges, rifle bullets, springs, metal tubes and timers. The devices, concealed in books, magazines and video boxes, all carry his signature - Mardi Gra.
His targets fit a pattern. First came Barclays Bank, where he struck a dozen times at different branches. Last month he switched to Sainsbury. In between were a few apparently random attacks on businesses, phone boxes and private addresses. All the bombs were planted either in the capital, mainly west London, or the Home Counties.
But police know next to nothing about the man himself. They are understood to have called in forensic pyschologists in an attempt to build up a profile of their opponent. Last week, the head of the investigation, Detective Superintendent Jeffrey Rees, said he believed someone could be shielding him.
So far, no one has been injured, although that appears to have been more by luck than design. Last weekend's device was particularly dangerous, and could have killed or seriously hurt. Mardi Gra - thought to be a misspelt version of the French term for carnival - seems to be escalating his campaign. The question is: how far will he go?
Equally puzzling is his motivation. It is likely that he suffers from paranoid delusions, and has become fixated in turn on Barclays and Sainsbury as sources of a perceived slight. He could be a sacked employee, or a businessman with a grudge. But the trigger, says Ian Stephen, a clinical forensic psychologist, could be extremely trivial.
"It could be something as small as being turned down for a Visa card, or being given the wrong change at a check-out," said Mr Stephen, a consultant to the television series Cracker.
He believes the bomber fits the classical stereotype of the shy, self- contained loner, socially dysfunctional but adept at leading a double life, whose family and neighbours would have no inkling of his secret obsession. His aim is to gain attention; his pleasure is derived from exerting power by remote control.
"He is holding these big companies to ransom, saying: 'I'll show them,'" said Mr Stephen. "He calls himself Mardi Gra - he seems to be having a carnival watching people run in circles while he pulls the strings. He's got the power to decide when to do something, and what to do."
Comparisons have been drawn with Theodore J Kaczynski, the suspected Unabomber,about to go on trial in America after an 18-year campaign. Kaczynski was arrested after his brother recognised phrases in a rambling 25,000-word statement that he sent to newspapers.
The only clue left by Mardi Gra is a chocolate and orange cake of a type sold by only a handful of retailers in the south-east. The cake, left in a carrier bag with one device, may be part of the game with police - a small lead to whet their appetite, a tease to their investigative skills.
Professor Paul Gilbert, a psychologist at the University of Derby, believes the bomber does not intend to cause harm, but would care little if he did. "He probably feels he is on a righteous mission, that he has to teach these people a lesson. There is nothing impulsive about it; it's all carefully planned."
Mardi Gra - who may have a military background, given his skills - has been through periods of intense activity, followed by lulls lasting several months. These may reflect build-ups of anger and frustration, which he purges. At the moment he is in a busy phase.
"You never quite know how dangerous these people are," said Mr Stephen. "He seems to be upping the game. But how far he will go is a matter of conjecture."Reuse content