He was once the debonair public face of the Gaddafi regime, the cosmopolitan second son who studied at the LSE, and brokered his father’s rehabilitation into polite international society.

In the early 2000’s, many Libyans also put their faith in him in, when it seemed that his push for ‘reform’ was the only way change would come to Libya.

Through his Gaddafi International Foundation he tried to lance the wounds of the past, arranging compensation for victims of the French airliner UTA 772, brought down in 1989, and for Libyan families who had lost relatives in the 1996 massacre at Abu Salim jail, in which Gadaffi’s forces gunned down 1270 prisoners.

All that changed on February 20th 2011, as the uprising against his father began and he appeared on Libyan TV, wagging his finger at his compatriots, shouting threats.

If this didn’t stop, he said, Libya would split along tribal lines and descend into civil war. It would be occupied by Britain and the USA.

Bread would become more expensive than gold. He accused the protesters of being drug addicts and fundamentalists.

“We will fight to the last man and woman and bullet,” he said, and every Libyan understood what he meant.

Within hours, armoured vehicles approached the square in Tripoli where protestors had gathered and fired large calibre rounds, some from anti-aircraft guns. Scores of people were killed, hundreds arrested.

Saif was never purely the liberal reformer he claimed. In a 2002 court case against the Telegraph for defamation – which, it must be said, he won – he produced a fascinating personal statement.

At 28, he was, he said, a normal young man whose interests included falconry, reading, painting, swimming, football and keeping pet tigers.

While studying in Vienna he had managed to persuade the head of the Schonnbrun Zoo to look after his rare Bengal tigers for him. This was not any kind of special favour, he said, but, “I was certainly delighted to have my tigers nearby because it meant that I was able to go and see them and play with them.”

Sometime later he fell out with the Austrian authorities who were reluctant to extend his residence permit.

“Fortunately, the Libyan government treated this insult to me very seriously and threatened to deny Austrians visas to enter Libya if the decision was not revoked,” he wrote. The decision was promptly revoked.

The men who captured Saif al Gaddafi are from Zintan, a town in the Nafousa Mountains west of Tripoli which rebelled against Gaddafi right at the beginning of the uprising and never looked back.

In August,  I travelled into Tripoli with the Zintan fighters as they took the capital. They were the heroes of the hour, but in recent weeks their reputation has been damaged by allegations that they have been stealing and misbehaving.

This is their chance to redeem themselves. If they treat Saif al Gaddafi humanely – in contrast to how the Misrata brigades treated his father when they captured him – it will boost their image and that of the new Libyan authorities.

And if Saif al Gaddafi, who is wanted by the International Criminal Court in the Hague, ever comes to trial we might yet learn more of the secrets of his father’s 42 years of dictatorship.

Lindsey Hilsum, Channel 4 News’ international editor, is currently writing a book about Libya. Follow Lindsey on Twitter @lindseyhilsum