Paris: Analysis of a windfall of data from inside Islamic State shows fighters of more than 70 nationalities joined the ruthless jihadist group, researchers said after examining thousands of records.
The treasure trove came from an IS defector who handed over some 11,000 personnel files to US television network NBC, although more than half were found to be duplicates.
NBC then passed 4,600 of the documents to the Combating Terrorism Center (CTC), which is based at West Point but independent from the US military academy.
The documents are one of several large-scale leaks from within IS this year.
Thousands of apparent IS registration documents were leaked in January to a Syrian opposition news website and in March the German daily Sueddeutsche Zeitung and German broadcasters said they had obtained similar records. German security services also had access to that material.
The CTC said that by comparing the documents it received from NBC against similar IS personnel records maintained by the US Defense Department, it was able to corroborate "approximately 98 percent" of them.
The forms, completed by recruits in Arabic and often including notes from the assessors, refer to around 30 percent of the estimated 15,000 new recruits who entered Syria during 2013 and 2014.
The analysis provided not only a composite picture of the fighters but also an insight into how IS is "attempting to vet new members, manage talent effectively... and deal with a diverse pool of recruits," said the report, which is available on the CTC website.
The recruits ranged in age from 12 to nearly 70, although the average age was 26 or 27.
Only 400 were under 18 upon entering the self-declared IS "caliphate".
The leading nationality with 579 new fighters, was Saudi, followed by Tunisian (559), Moroccan (240), Turkish (212), Egyptian (151) and Russian (141).
There were 49 from France, 38 from Germany, 30 from Lebanon, 26 from Britain, 11 from Australia and seven from Canada, but none from the United States.
Thirty percent said they were married, while 61 percent were single, with another eight percent unknown.Some 1,371 said they had finished high school while 1,028 said they had attended university.
"The group seems overall to be generally well-educated, especially when compared to United Nations data on the average years of schooling in the countries in the dataset," the report said.
The forms showed that IS intake officers interviewed the new recruits to assess their suitability for a range of roles in its apparatus.
"While the Islamic State needs some suicide bombers, it also needs personnel to fill roles like conventional soldiers, sharia officials, police and security or administrative positions," the CTC report said.
Thus one personnel officer wrote of a new recruit: "Important: he has experience in chemistry."
But when a 24-year-old Turkish entrant said his professional experience was as a drug dealer, the remark was: "May God forgive him and us!"
Nearly 10 percent reported having waged jihad previously, including a Frenchman who said he fought in Mali, while only 12 percent said they were prepared to carry out suicide attacks.
The cache also included 431 "exit forms" for departing jihadists, with reasons for leaving including the need for medical treatment, usually in neighbouring Turkey, or for family reasons.
Other remarks included simply "lied" for two of the fighters; "If he comes back again, he`ll be imprisoned"; "could not practise patience"; "does not want the military life and jihad"; and "confusion with matters".
More sinister were exit forms noting: "Go back to Libya and organise the way for the State"; "A task" and "Omar al-Shishani charged him with a job in Turkey".
Shishani, or "Omar the Chechen", who was effectively IS`s defence minister, was killed last month.
One line on the entry form is left blank, initially at least: Date and place of death.