LONDON, England (CNN) -- Eleven of the 22 people still being held over an alleged plot to bomb trans-Atlantic airliners have been charged in the UK with terrorism offenses as police revealed they have found bomb-making equipment and martyrdom videos.

Counter-terrorism prosecutor Susan Hemming said a 23rd person who was being held, a female suspect, has been released.

Of the 22 still being held, Hemming said eight were charged with conspiracy to murder and preparing acts of terrorism; a 17-year-old was charged with with possessing articles useful for acts of terrorism; and two were charged with failing to disclose material assistance in preventing an act of terrorism.

The other 11 are still being held without charge.

British authorities initially arrested 24 suspects on August 10, after revealing the plot to blow up airliners heading from Britain to the United States. Since then, two suspects -- including the woman -- have been released.

The charges stem from a cache of information seized during the months-long investigation into the plot, including "highly significant video and audio recordings" taken before August 10, Deputy Assistant Commissioner Peter Clarke said.

Those recordings include what are called "martyrdom videos," Clarke said.

British authorities have carried out a total of 69 searches of residences, businesses, vehicles and open spaces, which have netted bomb-making equipment and chemicals such as hydrogen peroxide, Clarke said.

"As well as the bomb-making equipment, we have found more than 400 computers, 200 mobile telephones and 8,000 items of removable storage media such as memory sticks, CDs and DVDs," he said.

"So far, from the computers alone, we have removed some 6,000 gigabytes of data."

It will take "many months" for investigators to analyze all of the data, he said.

In Pakistan, law enforcement authorities continued to interrogate Rashid Rauf, a Briton of Pakistani descent, over his alleged key role in the plot, officials told The Associated Press.

Pakistani Interior Minister Aftab Khan Sherpao said British police were conducting inquiries in Pakistan but were not involved in questioning Rauf.

Details of the investigation were revealed as Home Secretary John Reid said police investigating the alleged plot have gathered "substantial material" as evidence.

Authorities say the suspects plotted to use liquid explosives on as many as 10 flights, using commercial electronic devices as detonators.

The alleged plot's disclosure earlier this month sparked heightened terror alerts in Britain and the United States and ushered in tighter security regulations on passengers.