'We'll search every grain of sand for Muammar Gaddafi'

His eyes burning, the former police colonel leant forward in his chair and described in a quiet voice what he would do to Colonel Muammar Gaddafi if his men were lucky enough to catch him.

Colonel Moftah al-Swiah, a wiry 38-year-old former detective, was in the police force in a town near Tripoli until he defected in February to become a commander in Libya's revolutionary army. Now he is using his investigative skills in the vast desert on the Algerian border in the biggest manhunt Libya will ever see.

"I would not kill him if I found him, I would put him in a cage and take him around Libya," the colonel said. "And I pray to God that it is we who get the chance to capture him; my men will not rest until they find that criminal." His "men" were in fact mostly battle-hardened teenagers, 50 young rebels who were at school or university when the revolution broke out.

Since then they have fought through the civil war, and now they have joined the hunt for Gaddafi in the desert. They know it could be as dangerous as anything they have faced since they took up arms.

The clue that set the former detective on Gaddafi's trail came as he interrogated an important regime supporter near Tripoli last week.

The man let slip a hint that Gaddafi's hiding place was somewhere near the town of Ghadames. The colonel will not disclose exactly who his informant was or what he said, but it was enough for him to jump into his pick-up truck and immediately drive south into the Sahara.

He outlined his mission sitting in the foyer of the Dar Ghadames, a hotel usually full of tourists at this time of year, but with none to be seen on Saturday. It had been taken over by the colonel's men, who propped up their machine-guns in the foyer before relaxing on the sofas ahead of their next desert foray.

"The blood of 14 martyrs who fought with us and died is on our conscience," Col al-Swiah said. "We are hunting Gaddafi because of them, so they can rest in peace. We will examine every grain of sand in the search for him."

In reality, less poetically, he was sending his men out to pick up Gaddafi supporters for interrogation.

When the colonel left to give his men their orders, Fathi Uoshi, the National Transitional Council's military chief in Ghadames who is in overall charge of the hunt for Gaddafi in the district, said: "He and his men had a hard time in the fighting; I think they feel guilty for surviving when their comrades died. That is what is driving them. We depend on men like them."

The hunt for the fugitive former leader was infused with new energy last week. Ghadames was flooded with NTC fighters from Tripoli and the north, after the interim government realised it had to do more to try to seal its western border. More Nato aircraft than usual were overhead, locals said, and the government sent a military aircraft to patrol the desert.

The town, eight hours' drive from Tripoli, is one of the last outposts on the edge of trackless sand seas and sun-baked mountain ranges in the vast and empty south; the wastes, traversed only by smugglers and Tuareg nomads, are an ideal hiding place.

Col Fathi, a former air force officer, was busy dealing with the messy aftermath of a tribal war that broke out in Ghadames two weeks earlier between Tuareg tribesmen, supporters of Gaddafi, and Arabs who had joined the revolution. Fifteen people died and the fighting threatens to re-erupt at any time, hampering an effective manhunt.

Col Fathi said he was exchanging information with Nato daily, and directing his forces, including 30 desert trackers, to search for signs of Gaddafi or other key regime figures making their way towards Algeria. Patrols have been sent along the unmarked border, no doubt spurred to greater efforts by the NTC increasing the reward on Gaddafi's head to $2?million.

"All the Nato technology is trying to pick him up, they are using the satellites, the listening devices," Col Fathi said. "But perhaps an old man who knows the ways of the desert will be the one to find him."

The last reliable sighting of Gaddafi was in Tripoli soon after the capital fell in August. He gave no inkling of his whereabouts in his latest message to the Libyan people, broadcast by a Syrian television station on Thursday, in which he urged them to "go out and march in their millions" against the "unbearable" conditions they faced.

The desert south of Ghadames seems one of the likeliest hiding places and potential escape routes: his wife, daughter and two sons fled into Algeria from there in August. Last week Hisham Buhagiar, a carpet tycoon turned Gaddafi-hunter, said he thought his prey was near Ghadames.

Rumour and speculation are buzzing across the south; one story has it that Gaddafi is paying his way with gold bars, each stamped with his image. Another said he escaped in a $5?million armoured BMW supplied by France when he was friends with its government, a car reputedly bristling with electronic-jamming devices and thus invisible to radar and satellites.

More likely is that he is being helped by Tuareg friends on both sides of the border. The nomads have long been supporters who were well-treated by his regime, and Gaddafi was said to have relied for guidance on a Tuareg soothsayer, who has since fled her home. An impoverished people who once ran the caravan routes across the Sahara, they know the desert trails, and Gaddafi may have paid Tuareg guides for help.

If Algeria's government - run by old friends - was prepared secretly to take him under its wing, it could offer him a protection that impoverished nations such as Niger or Mali, also spoken of as possible refuges, could not.

"If he is still in Libya, Gaddafi probably travels in convoys a lot smaller than the ones he used to use," said Abdelrahman Busin, a spokesman for the NTC's forces, now the National Liberation Army.

"He probably doesn't move much, and when he does it must be under the cover of dark, discreetly and quickly. He may still have hundreds of loyal supporters, many motivated by money, although they probably function as a spy network. He cannot afford to draw attention to himself."

For the NTC, catching Gaddafi is just one among a series of competing priorities. But Mr Busin added: "As long as he is alive and roaming free we must expect the possibility of his supporters launching terrorist attacks."

Senior officials in Ghadames are urgently trying to mend relations with the Tuareg. "I visited the Tuareg refugees who have fled Ghadames and told them if you catch Gaddafi, you will be number one," said Sharif Abdulmula, 33, Col al-Swiah's field commander. However, many were still unwilling to turn against their former ally. Commander Abdulmula, in the Sahara for the first time, knows how much he needs their help; he was organising a four-day patrol into the desert with his men who, like him, were all from the cities of the coastal north.

"It is very dangerous, with a big risk of ambush," he said, stroking the bushy beard he has vowed to shave only when Gaddafi is captured.

Without the Tuareg, it may have grown a lot longer before that happens.