Kenneth Williams: trained sniper, Little League coach and tenacious FBI agent

Kenneth Williams – author of the "smoking gun" memo at the centre of the terror warning furore – is said to be a dedicated and relentless officer, dogged in pursuing even the smallest clue in a case.

He has been an agent at the Phoenix office of the FBI for 12 years, having previously served as a police officer in San Diego, California, and in a SWAT police paramilitary unit. While sharp and hard-working, he is said to be mild-mannered. In his spare time he is a Little League baseball coach.

After 11 September, Mr Williams, 41, was working 18 hours a day in pursuit of leads. "He's just a good, good guy – a very dedicated, very tenacious agent," said Roger Browning, a retired FBI agent and Mr Williams's supervisor for more than five years.

Earlier this year, Mr Williams testified in court against a Saudi Arabian pilot accused of lying about his association with Hani Hanjour, a hijacker of American Airlines Flight 77. In court he identified himself as the FBI's lead agent in Arizona on the case of the Pentagon attack, and said he had been working on Islamic terrorism for 11 years. His partner, George Piro, is the only FBI agent in Arizona who speaks Arabic.

In that testimony, Mr Williams – also a trained sniper – said: "The smallest bit of information that comes in could later turn out to be the most important piece of the investigation". He also played a key role in the 1995 arrest of Michael Fortier, who helped Timothy McVeigh plot the Oklahoma City bombing.

Mr Williams' memo last July referred in detail to eight Middle Eastern flight school students he believed had indirect links to al-Qa'ida and he recommended that all foreign flight students be screened. But last week, Mr William told lawmakers on Capitol Hill that he never expected his superiors to react to his suggestion immediately.

Indeed, he said he marked his memo "routine", knowing that it typically takes 60 days for such documents to go through the chain of command at FBI headquarters. The memo never made it past the FBI's counter-terrorism division, where it was quickly rejected as unworkable and speculative.

Mr Williams is also at the centre of allegations that agents in Phoenix mishandled a Chinese spy case and an undercover attempt to collect information about Palestinian terrorist organisations abroad, according to court papers.

For two years, Harry Ellen, a intelligence informant, has been asking the FBI to investigate his complaint that Mr Williams and other Phoenix agents endangered his life by blowing his cover to foreigners whom Mr Ellen was helping the FBI monitor.

Andrew Buncombe