TIMBUKTU, Mali (Reuters) - Residents who slipped into a non-descript mud-brick house after Islamist fighters fled Mali's desert town of Timbuktu uncovered a trove of arms, ammunition and documents - the workings of the local al Qaeda recruitment office.
"We found lots of IDs, passports and birth certificates," said El Hadj Garaba, who searched through the house with neighbors before French intelligence officers arrived.
The documents - from Mali, nearby African nations and distant countries like Saudi Arabia and Britain - suggest the Islamist groups used their 10-month occupation of northern Mali to stretch their tentacles across West Africa and beyond.
Their recruitment drive suggests the French-led war against al Qaeda and its allies could drag on long after France starts withdrawing from Mali next month, spilling across borders and destabilizing the broader region as Islamist groups fragment.
Two months in, the offensive has wrested northern Mali from Islamist occupation, killed scores of fighters and driven survivors into mountain caves and desert hideaways stockpiled with arms and supplies.
But the documents - alongside interviews with residents of liberated towns - show that Islamist ranks, previously dominated by North Africans led by veterans of Algeria's civil war, have been swelled by hundreds of fighters from Mali and neighboring countries - brought together by opportunity as well as ideology.
Garaba listed Mauritania, Niger and Nigeria amongst nationalities represented. "But there were lots from Mali - including from the south," he added, picking through a courtyard still scattered with ammunition cases but now occupied by goats.
When France launched airstrikes in Mali on January 11, it billed its dramatic intervention as a bid to prevent Islamists seizing control of the whole of the landlocked nation of 16 million people and using it as a base to launch attacks on neighboring African countries and the West.
The French-led campaign has dealt the Islamists a heavy blow, killing many of their leaders. The reported death of Abdelhamid Abou Zeid, one al Qaeda's top regional commanders, in the Amettetai Valley would be a major scalp, if confirmed.
But the risk remains of the Islamists, particularly their new West African recruits, melting away into neighboring countries and regrouping once offensive operations ease up.
"Abou Zeid's death will decapitate them but they'll find new leaders," an ex-senior Malian intelligence official said. "Their ideas have spread. They'll probably split into smaller factions."
Algerian-born Abou Zeid and Mokhtar Belmokhtar, another top Islamist whose death was claimed but not confirmed, led the two southern units of al Qaeda's North African wing, AQIM.
Operating across the Sahara, south of the main body of fighters in Algeria, their bands found wealth and notoriety by kidnapping Westerners for ransom and exploiting smuggling networks criss-crossing the vast stretches of desert dunes.
In the process of exchanging goods and services with remote Malian communities abandoned by the state, they forged personal and ideological ties that would prove crucial to their takeover of the country's desert north - an area the size of Texas.
"What you had was a slow indoctrination of their beliefs. It wasn't just a 10-month brainwashing -- it had been going on for years," said Rudy Atallah, a former senior U.S. counter terrorism official focused on Africa. "It wasn't the bulk of the population but they reached out to some people, no doubt."
Fighting alongside and then hijacking a Tuareg separatist rebellion launched early last year, the Islamists stitched together a patchwork of groups mixing ideology and criminality that then carved up northern Mali.
France's liberation of Timbuktu and Gao in late January was greeted with jubilation by flag-waving residents, who had been forced to endure months of strict sharia Islamic law, including whippings and amputations of limbs for certain crimes.
Residents are now enthusiastically helping security forces identify fighters and collaborators. But elders in Timbuktu and Gao paint a more complex picture of life under the Islamists.
Arab communities in both towns, who had a history of collaborating with AQIM, helped to engineer the Islamist takeover and backed the occupation, partly in order to protect their own interests.
When Islamists seized power, sidelining the unpopular and ill-disciplined Tuareg separatists who had looted and pillaged, they also enjoyed a degree of popularity with the broader black African population that channeled in recruits.
Abdelmalek Droukdel, the Algerian emir of AQIM, urged his fighters last year to integrate with local tribes and cautioned against imposing sharia too abruptly. For a while, it seems, they followed his advice.
Mahamane Qoye Tandina, a senior member of Timbuktu's crisis committee that met regularly with Abou Zeid, said Islamists successfully played on conservative strains in society.
"Some people appreciated that they wanted to change girls' behavior and cut back on alcohol and tobacco," he said. "But when they started to chop off hands, they went too far."
In Gao, Soumeylou Maiga, head of programming at Radio Aadar Koima, said the Islamists tricked residents, promising to replace a distant government that had abandoned them and to respect their moderate form of Islam.
"This helped them get recruits. They went to the madarassas and recruited people without jobs. They took aid and got recruits in return," he added. "For some it was about religion. For others, it was about the money."
New York-based Human Rights Watch documented the recruitment of hundreds of children in the Gao and Timbuktu region.
A young recruit could earn about $300 per month, residents said, a huge sum for the desert north's stagnant economy.
In both towns, Islamists made locals the face of the occupation -- though foreign fighters retained leadership.
In Timbuktu, it was Sandou Ould Boumana, a Malian Arab from the trading town. Although an established member of AQIM, he spoke in the name of Ansar Dine, a Malian Islamist group.
In Gao, Aliou Toure, a Songhai, went from trading animal skins in the towns market to head the feared Islamic police.
One of the starkest changes was the rise of MUJWA, whose name - the Movement for Unity and Jihad in West Africa - reflected its aim of breaking with AQIM leadership dominated by veterans of the Algerian civil war.
The mix of black Africans from Mali and neighboring countries recruited in the MUJWA's fiefdom of Gao pointed to a degree of success.
A Malian intelligence officer said Islamists' identity cards seized in Gao came from countries including Togo, Tunisia, Burkina Faso, Algeria and Niger.
Seid Abdoulaye Toure, a senior local imam in Gao, said the MUJWA cleverly targeted the region's poor who had been exposed to some Islamic education in Koranic schools but lacked the ability to question the form of Islam being imposed.
"The reality of the problem is here. We should not look too far," he said.
Many in Gao look just across slow-moving, brown waters of the Niger River to a small town called Kadji.
The village contains one of the pockets of ultra conservative Wahhabist Islam that have existed in Mali for decades, fed by an influx of foreign preachers.
"All the youth from there were with MUJWA," said Zouhairou Kowa, a Kadji resident, referring to the Dar es Salaam neighborhood. "They took them into the hills, they trained them and they came back."
Before the offensive, which Paris says has killed hundreds of rebels, it was estimated there were 2,500-3,000 Islamist fighters in Mali. The U.S. military estimated 800-1,200 of these were hardcore jihadist.
Prisoners captured during the French-led offensive highlight the increasingly broad make-up of the Islamist ranks. A Reuters reporter travelling with Chadian forces in Tessalit earlier this month saw eight captured Islamist fighters from Morocco, Tunisia, Burkina Faso and Nigeria.
For years, intelligence sources have said militants from Nigeria's Boko Haram have linked up with Islamists in Mali for training, though the group has remained largely focused on its fight to impose sharia law in northern Nigeria.
In recent weeks, however, Boko Haram statements point to some factions becoming more ideologically aligned with international jihadists.
Gunmen claiming to be from Boko Haram cited France's military offensive in Mali as justification for their kidnapping of a French family of seven in Cameroon last month.
Ansaru, a Boko Haram splinter group which said it executed 7 hostages last weekend, has also directly allied itself with international jihad.
January's mass hostage taking at Algeria's In Amenas gas plant, masterminded by Belmokhtar, showed the ease with which militants can glide across regional borders.
Andrew Lebovich, a Sahel analyst, said the make-up of Belmokhtar's group and the routes used in the attack pointed to cooperation between militants in Mali and Libya.
This challenges the perception of Mali's conflict as principally threatening the Sahel - a 5,400-km band running east-west across Africa, south of the Sahara desert.
Islamist activities fanning north and south from Mali to Nigeria, Algeria and Libya have raised concern among British officials. "We don't see it as a threat to London or Birmingham but we have a lot of interests in that region," said one.
For now, France and its African allies are still finding out if the Islamists' new recruits and foreign links will allow them to survive the unprecedented offensive on their positions.
"Will they have had the time to become hardliners? I don't know," said one senior West African official, who has had direct contact with the armed groups in recent years.
For now, the battle appears far from over.
"If the Islamists are able to keep moving, hiding, it will be endless war - like Afghanistan," said one Western security official with years of experience in the region.
Additional reporting by Joe Penney and Emmanuel Braun in Gao, Madjiasra Nako in Tessalit; Editing by Daniel Flynn and Anna Willard