Anti-terrorist officers are drawing on the skills of the FBI and forensic psychologists in an attempt to get inside the mind of the man who calls himself "Mardi Gra".
Details emerged yesterday of an obsessive man who has gone to extraordinary lengths in his 16-month campaign against Barclays. He appears to have taken a great pride in his work - bombs have been meticulously packaged and he has used distinctive logos and wording.
As in the case of the American "Unabomber", who waged a war against technology, Carol Sellers, a forensic clinical psychologist, believes money is almost certainly not Mardi Gra's main motive. She said: "With most people who get involved in blackmail it's a one-off thing, because they don't want to get caught.
"Where somebody keeps making demands this suggests a more psychological element. I would say this person has a deep rooted grudge, a concern about something that happened in the past.
"He could be a former customer, an ex-employee who was made redundant, or even a businessman whose business was foreclosed.
"The case is most unusual because of the sheer persistence of the individual concerned. Whatever happened is psychologically very important to this person."
She said it was clear the bomber wanted publicity and the wish to be noticed was probably more important than any desire to hurt. But Ms Sellers warned if causing injury resulted in more publicity, it might spur the bomber on to take more extreme action.
She added it would be wrong to assume the bomber was mentally ill.
"He is rational enough to organise an elaborate campaign," she said. "This is not someone who is mentally ill in the conventional sense."
That ability to carry out careful planning is shown in his demand that Barclays give him credit cards with special PIN numbers that would allow him to withdraw unlimited amounts of money from automatic cash machines. This is a similar ploy to the one devised by Rodney Witchelo, the former policeman who tried to extort pounds 4m from Heinz. Witchelo was jailed for 17 years in 1990 for spiking jars of baby food on supermarket shelves with bleach and razor blades.
The difficulties of handling and tracking down a blackmailer who targets a big business rather than an individual were examined last month by security consultant Brian Worth, a former Metropolitan Police deputy assistant commissioner.
Writing in Intersec, a security magazine, Mr Worth listed the typical characteristics of prosecuted corporate extortionists.
Perpetrators tended to be, lone men aged 30 to 50, with some business acumen, although often the business had failed. The person is also likely to be someone with no previous convictions and no connection with traditional criminals. They often make a "once and for all" extortion attempt and start out with no initial intention to harm.
The extortionist may also have experienced a "learning curve" - getting valuable lessons on how to pursue a campaign from previous, aborted extortion attempts, and may well have had some kind of inside information about the target business.