Beijing: Lawyer Li Zhuang remembers the snap as police buckled him into a "tiger seat", an instrument for sleep deprivation that he said was a staple in the crusade against organised crime that won fame for China's now fallen leadership aspirant Bo Xilai.

Li has been the most outspoken lawyer to challenge Bo's crackdown on crime syndicates, an offensive that boosted Bo's nationwide popularity and hopes for climbing from his base in Chongqing, a huge city in the south-west, to the centre of power when China's new leadership is chosen later this year.

‘Such barbarity'

That campaign could now figure in the aftershocks to Bo's abrupt downfall this month, as allegations increasingly emerge of widespread torture in Chongqing, adding to accusations that Bo became a law unto himself.

"I never expected that there would be such barbarity, such flouting of the law, such reckless, brazen violation of the law," Li said of Bo's anti-crime campaign.

Li is also a critic of Bo's long-time police chief Wang Lijun. Wang triggered both his own and Bo's downfall by fleeing to a US consulate on February 6 where he hid for 24 hours until Chinese officials coaxed him out. The reasons for Wang's flight to the consulate remain unclear.

The 50-year-old Li was convicted and jailed in early 2010 after vigorously defending a client on trial in Chongqing's anti-gang campaign. Li ended up being charged with persuading his client falsely to claim torture.

‘Rolling war'

"From what I've heard, the longest that someone was held and not allowed to move was ten days. I sat in one for three days and three nights," Li recalled of his time in a "tiger seat," after he was arrested by Chongqing police.

The chair is screwed to the floor, with belt and braces to immobilise suspects bolt upright so police can keep them awake, creating deep exhaustion, Li said.

"All those who were arrested were deprived of sleep for the first few days. In torture parlance, it's called a ‘rolling war', so you're deprived of sleep and utterly exhausted," he told Reuters in a sometimes tearful interview in Beijing.

"It was interrogation across dozens of hours on end," he added, noting that he was allowed toilet breaks.