It was an unexpected but happy situation. Accordingly, the brakes have been put on the completion of the Changi Prison Complex. Prisons director Ng Joo Hee said two of the four clusters will not go up for now. It is money saved too, given the dizzying rise in construction costs.

So why the lower numbers?

One reason: fewer 'returnee' prisoners. In 1998, almost one in two freed prisoners were back in jail within two years. In 2005, only one in four went back.

Getting the drug situation under control helped too. In 1997, drug rehabilitation centres housed 5,508 abusers. Last year, just 451 were locked up.

Mr Ng offered a third reason: 'In an ageing population, you generally see a lower crime rate. Therefore, there is lower incarceration.'

The crime rate last year was 696 per 100,000 people, a drop from 974 in 1997.

One other factor: The courts have been slower to pack convicts to jail. Senior lawyers like Mr T. U. Naidu noted judges have become more open to other sentencing options like probation.

Work on the $1 billion complex, on a 49ha site off Upper Changi Road North, started in 2000, with the old Changi Prison later pulled down to make way for it.

It was reported then that a centralised jailhouse - which would replace the 14 jails then operating - would ease the overcrowding problem. It would also cut costs, speed up work and boost security.

Mr Ng said: 'We're probably the only jurisdiction in the world of a decent size to put all our prisoners in one place. We do this because land is precious and we can return some of the land.'

One cluster of blocks has already been completed, with over 5,000 occupiers from three defunct prisons - Changi, Jalan Awan and Moon Crescent - housed there.

A second similar cluster will be up by next year. It will house inmates from five more prisons, including Queenstown Remand Prison and Tanah Merah Prison.

Given the overcrowding problem prisons elsewhere face, Singapore is in 'quite a good situation', said Mr Ng. This means more attention can be devoted to rehabilitating prisoners.

He said ensuring that inmates do not re-offend is key, as about 11,000 of them are released every year. Hence, the importance of initiatives like the Yellow Ribbon Project and a slew of work programmes to help ex-convicts return to society.

'It's really the smart and practical thing to do. We don't just do it because we've bleeding hearts...we do it because we want to reduce harm in society.'

One 'very special group' the Prisons is focusing on is young inmates aged below 21, who numbered 550 last year. They will get more chances to advance their studies while serving their sentences.

Mr Ng said: 'We've a golden opportunity to give them education. They have their whole lives ahead of them. If we don't do anything for them, they could well be on a lifetime of crime.'

The need for the last two clusters will be reviewed every year. What might be erected instead: A detention centre for Internal Security Act detainees, following a recommendation made in the wake of terrorist Mas Selamat Kastari's escape from the Whitley Road Detention Centre.

Planning for this will take time, said Mr Ng, adding: 'It's a work in progress.'