The horrific scene 15-year-old Baba and his comrades encountered, a week after the kidnap of Chibok girls early on April 15, was in thorny scrubland near the village of Ba’ale, an hour’s drive from Chibok, where 276 girls aged 16 to 18 were taken from their boarding school dormitories with 223 still missing. It was still two weeks before social media campaigns and protests would prick the Western world’s conscience over the abduction.

The tiny rural village, halfway between Chibok and Damboa in the besieged state of Borno in Nigeria’s north-east, had been helpless to stop the Boko Haram gang as it swept through on trucks loaded with schoolgirls they had taken at gunpoint before torching their school.

Venturing further up the track, Baba and his fellow vigilantes found the two girls tied up to a tree by me of Boko Haram. Baba, the youngest of the group, stayed back as his friends took charge. ‘They used my knife to cut through the ropes,’ he said. ‘I heard the girls crying and telling the others that they had been raped, and just left there. They had been with the other girls from Chibok, all taken from the school in the middle of the night by armed men in soldiers’ uniforms.

‘We couldn’t do much for them. They didn’t want to talk to any man. All we could do was to get them into a vehicle and drive them to the security police at Damboa. They didn’t talk, they just held on to each other and cried.’

This grim scene was discovered by 15-year-old Baba Goni. ‘The girls sat on the ground at the base of the trees, their legs stretched out in front of them, they were hardly conscious,’ says Baba, who acted as a guide for one of the many vigilante teams searching for the Nigerian schoolgirls abducted from their school last month by Boko Haram and now at the centre of a concerted international campaign for their freedom.

In the days following their disappearance, rag-tag groups such as Baba’s, scouring the forests in a convoy of Toyota pick-up trucks, were the girls’ only hope.

But hope had already run out for some of the hostages, according to Baba, when his group spoke to the terrified inhabitants of the village where Boko Haram had pitched camp with their captives for three days following the kidnap.

The chilling account he received from the villagers, though unconfirmed by official sources, represents the very worst fears of the families of those 223 girls still missing.

Four were dead, they told him, shot by their captors for being ‘stubborn and unco-operative’. They had been hastily buried before the brutish kidnappers moved on.

‘Everyone we spoke to was full of fear,’ said Baba. ‘They didn’t want to come out of their homes. They didn’t want to show us the graves. They just pointed up a track.’

For Baba, a peasant farmer’s son who has never been out of rural Borno, it was shocking to see young girls defiled and brutalised by the notorious terrorists he knew so well.

But his own life has been full of tragedy and he told how he had ‘seen much worse’ than the horror of that day in the forest.

A bright-eyed Muslim boy from the Kanuri ethnic group, proud of a tribal facial scar and nicknamed ‘Small’ by all who know him because of his short, slim frame, he described a happy childhood with three brothers and two sisters in Kachalla Burari, a collection of mudhouses not far from Chibok.

Without electricity or running water, the children spent their days helping on their father’s subsistence farm, planting maize and beans and millet.

Baba and his friends used home-made catapults to shoot birds and in the rainy season fished in the river with bent hooks. But by his tenth birthday, the scourge of the radical Islamist Boko Haram was creeping up on everyone in Borno State.

Baba and his siblings attended a local madrassa, or religious school, where they learnt the Koran, but he had no formal teaching and cannot read or write to this day.

By 2009, Boko Haram were becoming active in his area, peddling their message of hatred to Christians, but also turning on Muslims they branded as informers.

Baba’s village life came under siege. There were attacks on the Christian population in the region, with bank robberies funding the gang. Disaffected, unemployed youths from local families were recruited and neighbours who once lived in peace now spied on one another.

One night as he slept in his family’s mudhouse in the village, the gunmen came door to door, looking for informers. ‘I heard some noise, I woke up and saw men coming through the door, shooting at my uncle who was in the bed beside mine,’ he said. ‘That was the end of my childhood, the end of everything. I saw his body covered in blood, I backed away, and the men turned their guns on me. They grabbed me roughly and took me outside to a pick-up truck.

Baba, telling his story confidently and lucidly, wants to skate over the details of his two hellish years in the Boko Haram camp in Sambisa Forest. Today there are special forces soldiers swarming over the vast nature reserve and circling overhead in surveillance aircraft.

For this slight boy, there was no such worldwide interest as he scurried back and forth at the command of a ruthless gang dug into woodland far from any help or rescue.

He remembers many of them lived with women who had come voluntarily into the camp. He never saw any girls abducted. This latest phenomenon is unknown to him. ‘There were many abducted boys, but no girls,’ he said. ‘We were all scared to death and had to do whatever we were told: fetch water, fetch firewood, clean the weapons.

‘We couldn’t make friends, you didn’t know who to trust. I was made to sleep next to the Boko Haram elders, the senior preachers. I had no special boss in the camp, I was ordered around by everybody’.

The men prayed five times a day yet would leap on their motorbikes and trucks to carry out killing sprees.

‘I knew they had started out as holy men but now I saw them as criminals, loaded with weapons and ammunition,’ he said.

As he got older, he was taught how to use an AK-47, how to strip it down and clean it, and reassemble it.

He could never understand what drove the men. They did not use alcohol or hard drugs, though he sometimes saw them smoking marijuana. They were monsters and he felt convinced they were mad.

‘They were wild, even when they prayed so loudly in groups together, making us join in. They were insane, unpredictable, and always planning their next attack. I never wanted to be one of them.

‘They slept rough every night, just taking shelter under trees in the rainy season,’ he said. ‘We all wore the same “afaraja” the Nigerian long shift and trousers day and night. We washed them when we could. We slept on mats made of palm leaves, out in the open with the trucks all parked nearby, ready for a hasty move if necessary.’

He said the fear, and the endless boredom, were his worst enemies. ‘They made us work hard so it was easy to sleep. I don’t remember crying through homesickness. I think the night when my uncle was killed in front of me did something to my feelings forever. It seems mindless, but I adapted to my life out there.’

‘He brought two of his senior men to stand beside me. He said I would be going with them to my family’s home and I would have to shoot and kill my father.’ Baba had no time to plan. He was sandwiched between the two fanatics as they set off on a motorbike for his village home.

‘I pretended I was willing to do the job. I took the ammunition belt I was handed and clung on as we drove through the rough bush. When we were less than a mile from a nearby village, I threw the ammunition belt to the ground and pretended it had slid out of my hands.

‘They stopped to let me pick it up. Instead, I ran as fast as I could through the undergrowth. I didn’t care about thorns or snakes or anything. They shot at me and I could hear the bullets flying past and hitting the trees, but I was not going to stop for anything. I made it to the village and some kind people let me hide there.

‘The shooting would have been heard by local vigilante groups. I think that is why I wasn’t followed by the men on the bike.’

The next day Baba went home. He saw his grieving parents and siblings for the first time in two years.

‘But I couldn’t stay,’ he said. ‘I was bringing danger to their door and we all knew it.’

Confirmation of that came when Baba soon heard that vengeful Boko Haram chiefs had put a bounty on his head for his defiance of the equivalent of £12,000 a fortune in the local economy.

‘I took a bus to Damboa, to report to the youth vigilante group,’ he said. ‘I wanted to work with them and I knew I was doing the right thing.’

His family, terrified, abandoned their home soon afterwards and today live in a remote part of Borno, rarely seeing their eldest son. He lives with a cousin who is also under a Boko Haram death threat.

He became a valuable volunteer with the vigilantes. He helps man checkpoints where Baba points out members of Boko Haram to the rest of the team.

But he was soon exposed to brutality of a different kind this time from the government side. He helped to get one of his captors, a man he only knew as Alaji, arrested and handed to the soldiers. ‘It felt good at first, but then they shot him dead right in front of me,’ he said.

Now joining the patrols armed with a shotgun and machete, Baba has been able to give valuable intelligence to the Nigerian authorities about Boko Haram’s way of life in their camps.

‘By now I have seen this violence many times. It never gets better. It will always be an even worse sight than finding those poor schoolgirls in the forest,’ he says.