Libya: ‘It’s all over’ - but how did it happen so fast?

Although heavy fighting continues around Col Gaddafi's compound, and his whereabouts remain unknown, the fall of Tripoli appears to have happened with astonishing speed. As the New York Times puts it, the rebels' advance into the capital yesterday "was more of a Sunday drive than a punishing final offensive".

This morning, Green Square, only recently the scene of highly orchestrated pro-Gaddafi gatherings, belonged to the people of Libya.

They tore down posters of Gaddafi and stomped on the image of the dictator who ran their lives for 40 years. One resident told BBC Radio early today, "I think it's all over... This is the day we have been waiting for."

• In pictures: Libyan rebels overrun Tripoli

Two of Gaddafi's sons – Saif al-Islam and Muhammad – are said to have been captured by the rebels, though neither man has been produced.

Gaddafi himself may or may not be in his compound. There are reports that South African president Jacob Zuma sent a plane earlier this month ready to evacuate him when he wished. It is not clear yet whether the Libyan leader has made use of it.

In the US, President Obama, holidaying on Martha's Vineyard, said Gaddafi "needs to acknowledge the reality that he no longer controls Libya" and step down immediately.

Here David Cameron has cut short his West Country holiday and returned to London to oversee a meeting of the National Security Council for Libya. He, too, has urged Gaddafi to relinquish power immediately, before any further blood is spilt.

How did Tripoli fall so fast? It is now clear that Nato has upped its game in recent weeks. There has been greatly increased US intelligence help in Tripoli while UK special forces have been more heavily involved in training and arming rebels than anyone realised.

According to Robert Fox, who writes on defence for The First Post, the key to the speed of yesterday's advance was that the infamous Khamis brigade, loyal to Gaddafi, did not put up a fight.

What happens now? Gaddafi needs to be found if he has not already fled. Rebel forces need to beware of what Gaddafi's men may have left behind in the way of snipers and booby-traps.

On the political front, the rebels need the people of Tripoli to provide interim leadership for the city.

Has the West learned from Iraq? The lesson of April 2003, when US forces arrived in Baghdad and didn't know what to do next, casts a shadow over the Libyan campaign. The difference is that Libyans themselves have taken the capital. It is considered essential UK and Nato forces and politicians remain in the background.

Who should help the Libyans, if not the West? A Guardian editorial today says: "There is plenty of evidence of commonsense, democratic instinct, idealism and decency, as well as professional competence, waiting to be tapped in Libya. Experience, however, shows how such elements can also be outflanked and wasted as more extreme forces scramble for advantage.

"It is Egypt and Tunisia, the two states which are Libya's neighbours – whose revolutions inspired Libya's own effort to rid itself of Gaddafi, and which would have most to lose if Libya lost its way – that will have a special, and perhaps a weighty, responsibility." ·