He attended a secondary school in Haverfordwest, Pembrokeshire from the age of 13 where he was an unpopular pupil but returned to America during the sixth form and went on the join the army.

More than 90,000 documents were published on the Wikileaks website this week relating to the war in Afghanistan, just days after Manning was charged with providing a film, called Collateral Murder, to the site showing a US Apache helicopter killing civilians in Baghdad.

The new documents included reports of at least 26 Afghan civilians - including 16 children - killed by British forces, as well as friendly fire incidents that claimed the lives of Afghan security personnel.

The Pentagon announced it had launched a criminal investigation into the leak, and described Manning, an army analyst, as a "person of interest".

Wikileaks has not confirmed that Manning was the source but Julian Assange, the site's founder, has said that he is prepared to provide him some assistance.

Jenna Morris, 23, a shop manager from Haverfordwest and former classmate, described Manning as "a trouble-making authority-hating computer geek" who spent most of his time at school using computers. Other classmates said he preferred his own company and had a difficult upbringing.

Manning, who was arrested in May, is expected to face a military trial overseas.

In an online chat with a computer hacker, Manning boasted that he had used blank CDs to download information.

He also claimed he had retrieved 260,000 diplomatic cables and a video of a US air strike in Afghanistan last year that killed dozens of civilians.

Experts said his job would almost certainly have given him access to the Secret Internet Protocol Router Network, which hundreds of thousands of US military personnel, civilian employees and private contractors have access to.