Insider knowledge

Drop site allegedly used by Mr Hanssen on Sunday

Urgent questions are being asked about how veteran FBI agent Robert Hanssen, who sold some of the US Government's most sensitive secrets to Moscow, operated undetected for many years.

According to senior intelligence officials, one reason is that Hanssen, who worked for the bureau for 27 years, knew the system so well that he managed to avoid arousing suspicion.

These kinds of cases are the most difficult, sensitive and sophisticated imaginable

FBI Director Louis Freeh

Revelations about his alleged role at the heart of the FBI's counter intelligence operations in the US, have come as a huge shock.

The bureau is now beginning to assess the potential damage wrought to national security.

'Very experienced'

Apart from being indicted for espionage, Hanssen has been charged with betraying three double agents working for the Americans from the Soviet embassy in Washington,

Two were executed when they returned to Moscow, while the third was imprisoned.

FBI Director Louis Freeh said Hanssen had managed to operate undetected because he was "a very, very experienced intelligence officer".

The New York Times commented: "The bureau's own security safeguards seem to have been gravely deficient.

FBI agents have began searching Mr Hanssen's residence

"Even someone schooled in deception ought not to escape FBI detection for better than a decade of dealing with Russian handlers."

According to an FBI affidavit, Hanssen took numerous precautions that only a trained counter-intelligence expert would follow.

He refused to meet Soviet (or later Russian) agents in person, either in Washington or abroad, knowing that these agents were often under surveillance and that foreign trips would arouse suspicion.

He only used code for dates and places, encrypted computer discs and refused to accept KGB radio transmitters or other spy devices, which, if discovered, would immediately incriminate him.

Alleged methods of protection

Used 'Ramon' as a code name

Routinely checked FBI records

Never met face-to-face with his Russian counterparts

Former FBI director William H Webster, who is assessing the damage to national security, said he knew the bureau's counter-intelligence "matrix" too well.

The FBI has acknowledged that a detailed review of its internal security is certain to find flaws in the FBI's procedures for ferreting out spies.

The Washington Post says one area that is likely to be scrutinised is the FBI's unwillingness to give lie detector tests to employees on a regular basis.

Mr Freeh has not disclosed how Hanssen was finally caught, but there has been speculation that he was betrayed by a Russian source, who handed over his entire KGB dossier to the US.

Four-month operation

After the FBI became aware that there was a mole, a joint investigation was launched by the FBI, CIA, the State Department and the Justice Department.

Hanssen was kept under surveillance for at least four months. His phone was tapped and his house searched in his absence.

FBI agents also covertly intercepted $50,000 in cash, which Russian intelligence officers are believed to have put into a secret location - a "drop" - for Hanssen to pick up later.

He was finally arrested on Sunday at a park in Vienna, Virginia, after allegedly dropping off a package of classified information for retrieval by Russian agents.