Victims tell harrowing tales of attacks, but clearest revelation may be the divisive politics underlying the five-year insurgency Why did the world ignore Baga attacks?

Yusuf Sarkin does not remember much about the massacre that drove him from the town where he was born. The gunfire and the screaming and the frenzy of bodies trying to outrun bullets flying through the sandy streets of Baga blended into one long awful blur. But another loop of horror keeps playing in his mind: that he let go of his terrified 10-year-old son’s hand.

Sarkin and his wife grabbed their four children and joined others fleeing Boko Haram’s murderous descent on the town on 3 January. The 51-year-old’s only thought was to reach the shores of Lake Chad, around which the fishing settlement is built.

Sarkin was clutching Adamu’s hand and his family started running. But when he reached the water, where panicked residents were piling into canoes, he looked down to see his son had disappeared. “Can you imagine the fear that makes you let go of your child’s hand?” he asked, his voice hoarse as he relived the memory. “What happened that day, the things I saw, are so terrible.”

Traumatised victims fleeing the fog of war have thrown up staggering figures for the four-day carnage that ensued; they are unlikely to know the true number of dead. But the massacre’s clearest revelation may be the divisive political undercurrent on which the five-year insurgency has thrived.

Rather than addressing the mounting death toll, Nigerian officials initially traded accusations with neighbours Cameroon and Chad, allies it nominally works with against Boko Haram. With some local officials putting casualties at up to 2,000, it took a week before the government gave its first response.

The military said the massacre was Boko Haram’s deadliest in its five-year insurgency, but it added that the reports of 2,000 dead “cannot be true”. It suggested they were part of a smear campaign.

“From all available evidence, the number of people who lost their lives during that attack has so far not exceeded about 150 in the interim. This figure includes many of the terrorists who were bearing arms,” army spokesman Chris Olukolade said, adding that there were ongoing ground and air offensives to retake the town.

But the psychological damage of the incessant attacks is indisputable. The massacre has not, so far, warranted comment from the president, Goodluck Jonathan. Months after 276 girls kidnapped by Boko Haram made global headlines – a fact which has barely featured in the campaigns of candidates jostling for election in February – a largely mute reaction from ordinary citizens points to a nation inured to violent deaths. Last year, around 27 Nigerians died each day from Boko Haram-related violence. Now the first march for Baga victims is being organised in Paris , where 1 million people poured on to the streets after the Charlie Hebdo attack.

With four days of almost unopposed carnage, the militants cemented their control of Nigeria’s eastern border with Chad. The brazen attack showed not only how a fleet-footed sect has run rings around Africa’s largest army but how far Boko Haram’s once clear-cut aims have been lost in a haze of bloodshed as it tightens its grip on a state where it once had popular support.

Two hours north-east of the Borno state capital, Maiduguri, on a road littered with burnt-out government buildings, lies the outpost of Baga. The town’s remoteness made it a haven for fuel smugglers and cross-border raids by Chadian rebels in the 1980s, leading to a multinational army mission being headquartered there.

A series of lonely low-rise buildings surrounded by barbed wire and sandbags, the base nominally included troops from neighbours Niger, Cameroon and Chad. But accusations and counter-accusations of corruption and sabotage soured relations, and by November last year, after an attack by Boko Haram that killed at least 40 fishermen, only Nigerian troops were stationed there.

“This was an important base for us and it made no sense for them to pull out like that,” said a Nigerian soldier who served five tours of duty in Baga and spoke on condition of anonymity to the Guardian. “The [latest] attack wasn’t a surprise attack.”

A military spokesperson from Niger, which has experienced attacks from Boko Haram, said its troops had withdrawn for “tactical reasons”. Neither the soldier nor the official clarified when the last international troops departed.

Dawn had not yet broken when the militants began creeping in. These days, being in the wrong place at the wrong time in Borno state can cost one’s life and Yusuf Ahmed, a vegetable trader who had driven from Maiduguri a day earlier, had a lucky escape.

After finishing prayers at around 5am, he noticed several camouflage trucks filled with men driving into the town. The occupants wore military fatigues, so when the gunshots began an hour later, Ahmed was not immediately frightened. “Being a Maiduguri man who is used to soldiers all over the place, I actually walked towards the direction which people said they were coming from,” he said.

Nearby, another group of men started erecting roadside barriers. Among them was 37-year-old Yusuf Idris, who bought a $40 (£26) home-made musket and joined his friends in a civilian vigilante effort after a savage assault in 2013 turned Baga into Nigeria’s new ground zero against Boko Haram. When they noticed a flurry of military activity, Idris and his men wanted to help. Nobody expected the coming carnage.

By the time Ahmed came upon the group of “soldiers”, he knew something was wrong. “I knew they weren’t soldiers because they wore military uniforms but no boots and berets,” he said. Some took off towards the market, throwing money, cattle and food into their trucks. “They were laughing and saying why should they pay for what is theirs by right. They were looting everything,” Ahmed said.

Another group homed in on the army base. With cries of “Allahu Akbar”, the militants began shooting in earnest. At the roadblock, Idris hoisted his crude rifle and prepared to fight against insurgents armed with AK-47s and rocket-propelled grenades. “All of a sudden another group who had overrun the [army] base came towards us, mounted on armoured tanks, and that was too much for us,” he said. Two of the vigilantes were shot dead. The others fled.

Soldiers battled back for almost nine hours before throwing away their weapons and running into the bush, witnesses and a local official told the Guardian. No reinforcements arrived, according to the soldier and another official.

Idris, the vigilante, ran into a house whose corrugated iron roof had caved in under an onslaught of bullets. He and a shellshocked woman called Hadiza sheltered there for three days while the marauding militants looted and burnt houses. At night the two curled up beside the bullet-pocked wall and fell into an exhausted sleep to the sound of celebratory gunshots. One morning Hadiza crept out to find water and never returned. By nightfall, Idris decided to run.

“When I reached the bush, I was relieved at first but then I saw bodies everywhere. I walked through five villages and each one I passed was empty except for dead bodies.”

Among the hundreds fleeing was Sarkin, the herbal doctor tormented by memories of his son’s hand slipping out of his own. After two days of trekking, a wound in his leg turned puffy and black under the burning desert sun. Sarkin kept looking for his children in the ragged crowd of refugees dying of thirst and exposure around him.

“I grew up in Baga, my children schooled there. It’s too painful to even cry when I think of what happened,” he said from the refugee camp in Maiduguri, where motorists who picked him up eventually dropped him. Each day he combs through the hundreds of new arrivals alongside a neighbour whose children often played with his own, but both men have slowly accepted that their families have probably been killed. His youngest son, Gari, is five years old.

“Nobody has seen them. I think I have to accept that they are dead,” he said quietly. “Right now my mind is confused, but when I have the strength I think I have to go somewhere else and start afresh. It’s the only thing I can do now.”

• Isaac Abrak contributed to this report from Abuja