Insurgents are generally quite good at ferreting out collaborators, or people they think are collaborators, and torturing them to death in very public ways. For this reason torturing suspected insurgents to coerce cooperation from the public is generally ineffective. People forced to choose between being murdered by the security forces and being murdered by the insurgency will do anything they can think of to escape. The only thing it accomplishes is increasing the torment and suffering of the population. Generally speaking occupying forces do not care and will continue to torture anyway, but the most effective method remains to treat your prisoners and intelligence sources with dignity. Insurgencies are generally impossible to combat with conventional forces because the occupying force is invariably made of up young people with no personal interest in the colonial project who are suffering constant trauma and alienation from their role as occupiers and oppressors. Inevitably some number of them will engage in atrocities of one sort or another and no matter how they try to engender good will they will lose support from the public.

The only successes in combating insurgencies have been accomplished with total merciless destruction. The US famously kills civilians in great numbers and designates any male between 16 and 60 as a combatant. The Boers were finally suppressed by concentrating them in camps to cut off the insurgents from all support. Many Boers died in those camps but the British were indifferent to human misery as they are in all cases. The Indigenous American nations were not completely subdued until the Bison were slaughtered almost to the point of extinction, denying the Indigenous plains people their key source of food and other essentials. The last revolts were finally suppressed when the surviving indigenous people were forcibly removed to some of the most marginal and inhospitable regions of the United States. In many other places the Indigenous people were simply exterminated. The Turks suppressed Armenian resistance by forcing a million people to walk through the desert with no food, water, or shelter, resulting in an incredible amount of death. The Prague Ghetto was razed to the ground. The Nazis never successfully ended Partisan activity across their territory, and in local areas where they were successful it was generally by cornering the partisans and exterminating them to the last fighter. In Algeria the increasing brutality of the French occupiers galvanized the Resistance and after years of fighting and an immense death toll the French occupiers were forced to retreat across the Mediterranean. The US utterly failed to suppress the Afghan resistance groups during it's 20 year long occupation, simply failing to realize that every person they killed was part of an extensive kinship network that was activated to seek revenge. The Houthis recently began peace talks with the Saudi/US coalition after enduring years of genocidal attacks on essential civilian food, water, and medical infrastructure, the Saudis having proven unable to subdue them and increasingly vulnerable to Houthi counter attacks. FARC was never defeated in the field and finally came out of the jungle after a negotiated surrender. The Mongols of the Great Khan's Horde famously suppressed rebellion by exterminating every single person in a city that rose up. There are still regions where they so thoroughly exterminated resisting populations that they remain unsettled to this day. Shining Path has operated for nearly thirty years before it's leaders were finally captured, and small successor groups are still active. In Vietnam the US routinely exterminated entire villages, flattened entire cities, and forced peasants in to concentration camps euphemistically referred to as "strategic hamlets", but still failed to completely suppress Viet Cong irregular fighters and ultimately lost the war. In Iraq the US's attempts to suppress Iraqi insurgencies were a decade long disaster. While the US had some successes the Iraqi civil war of 2006 saw sectarian death squads exterminating or forcibly displacing entire neighborhoods of their enemies. When the US did have real successes it was often in situations where they were able to draw insurgents in to hopeless pitched battles, then unleash heavy artillery and airstrikes while claiming civilians had left the area. In Fallujah the US notoriously used tanks to drop entire buildings with point blank HE rounds, while clearing alleys by firing nets of high explosives normally used for mine clearence then setting them off to frag the entire street. Despite murdering hundreds of thousands to over a million people in their occupation the US non-the-less failed entirely and ISIS arose to terrorize the region shortly after the majority of US troops were withdrawn

This is a consistent pattern with insurgencies against colonial occupiers - The occupying forces frequently fail to suppress the insurgency, and where they do it is only with tremendous violence and destruction, if not a campaign of total extermination. The COIN community generally regards extermination of the population to be the only reliable and effective method of counterinsurgency, but they are usually restricted from enacting it due to prevaricating leaders who need to disguise their brutality to retain public support. This often results in insurgencies that stretch on for years or decades until the occupying forces are so thoroughly demoralized and the occupying nation so sick of war that the occupiers withdraw.