How much progress have the intelligence services made?

Until last Thursday, the investigation into who was responsible for organising the US terrorist attacks appeared to be going well. Too well, thought those familiar with the inability of the Western intelligence agencies to make any serious inroads into Middle Eastern terrorism. This was merely one in a long list of outrages, few of which had been followed by quick and successful investigations.

Too well, wondered those on this side of the Atlantic used to the authorities' rush to be seen to achieving results in the aftermath of IRA atrocities in Birmingham, Guildford and elsewhere.

Soon after the planes crashed, the public was told, all 19 hijackers had been identified; many of them were linked; agents were poring over their lives; everything pointed to a network controlled by Osama bin Laden. It was breathless, giddy stuff. Odd niggles presented themselves. Within hours of the suicide attacks, the FBI said it had made impressive progress, identifying hotels, car rental firms, houses used by the hijackers, but then the stream of information from the investigation dried up.

The FBI said it had identified all 19 hijackers – but, curiously, did not release all their photographs. In what was hailed as a breakthrough (the US press and by extension, much of the British, has been hailing breakthroughs ever since the inquiry swung into gear), the passport of one of the hijackers had been found near the disaster site in New York. Strangely, it was not put on display.

Closed circuit TV cameras operated at all the airports involved, yet few pictures of the hijackers on their way to committing mass slaughter were made available.

Mohamad Atta, who was visible on CCTV, and who had left sufficient clues for investigators to trace at least some of his movements, was named as the likely ringleader by the FBI. No evidence was released to back up this assertion of his seniority – indeed, there appeared to be nothing distinguishing him from any of the others, except his photograph was clearer than theirs and parts of his recent past were easy to fill in.

Across America and in Europe, people connected to the hijackers were arrested, but just as quickly they were released.

Reports were published of other planned hijackings that had to be aborted once the US shut down its airspace on that fateful Tuesday morning. Police said they wanted to locate one group of men who left in a hurry, after a flight due to take off at around the same time as the pair that crashed on to New York was grounded because of a mechanical fault. Despite this "breakthrough" the men have yet to be caught.

Then, last Thursday, Robert Mueller, the FBI director, admitted it had all been going too well. After previously saying he had "a fairly high level of confidence" his staff knew the names of all the hijackers, he now said that was not the case. "We have several hijackers whose identities were those of the names on the manifests. We have several others that are still in question. The investigation is ongoing and I am not certain as to several of the others."

This was quite a different Mr Mueller from the one witnessed before. Not so sure-footed, not so bullish.

Officials refuse to say how many of the hijackers employed false identities. At least six of the men named by the US as having taken part and died are alive and well and residing in Saudi Arabia – such as Abdulaziz Alomari, said by the FBI to be in the gang that flew the first plane into the World Trade Centre. Mr Alomari is an engineer in Saudi, having returned home from the US. In 1995, he reported that his apartment in Denver, Colorado, had been broken into and his passport stolen. According to the Saudi embassy, another five of its citizens had been horrified to discover they were supposed to be dead, having destroyed at least 6,000 lives. Mr Mueller's public disclosure echoed what those close to the investigation are saying in private: this will be a hellishly difficult case to crack.

There are 4,000 field FBI agents aided by 3,000 backroom staff working full time on the inquiry. Other US law enforcement agencies have also been drafted in, as have those of other countries. They face enormous problems.

The hijackers were Arabs. Few US law investigators understand Arabic. Names are misspelt, leading to officers charging up blind alleys.

Much has been made of the vast technological arsenal at the FBI's disposal. But eavesdropping and tapping phones are any good in an investigation only where the subjects are still alive. Nobody was listening in when the hijackers discussed their attacks. Now officers have to find someone to monitor.

This was not, in any sense, a normal crime. Unlike bank robbers or other criminals, the hijackers knew they would be identified; they fully expected investigators to pinpoint who on the planes was to blame. They knew they were not coming back so they left some clues – but only some. Computer equipment has been recovered from those close to some of the hijackers but, so far, not one email has yielded anything of value.