'Whether it is because of the Department of Justice's poor judgment or their bowing to pressure from the police, I really don't know.'

Elizabeth Tang Yin-ngor, spokeswoman for the Hong Kong People's Alliance on WTO, said that, given the weak evidence, the prosecution had been a waste of taxpayers' money.

She called for an independent investigation into the procedures used by senior officers.

'The whole investigation was conducted in a rough and careless manner, and the police have not been following their protocol in the identification process,' she said.

Chairman of the Police Inspectors Association Tony Liu Kit-ming said officers had done their best to fulfil their duties.

Fourteen of the 1,000 protesters arrested over the anti-globalisation riots on December 17 were charged, but the charges against 11 were soon dropped. Of the three South Koreans left facing prosecution, one, Yang Kyung-kyu, had the charges against him dropped six weeks ago and another, Park In-hwan, was formally acquitted of unlawful assembly last week after Magistrate Andrew Ma Hon-cheung ruled he had no case to answer.

Yun Il-kwan was acquitted yesterday, and said justice had prevailed.

The South Korean farmer hoped the day would be remembered as one when the injustices of the World Trade Organisation had been dealt a heavy blow.

Cardinal Joseph Zen Ze-kiun once again raised the ire of police officers by repeating his statement, first made in December, that he was 'ashamed' by their handling of the protests and saying the acquittals had validated his initial comment.

'You can understand why I had to do that,' he said. 'I think the one who made such a decision was mistaken and that was obvious. To arrest so many people without evidence, without concern for their needs, was a mistake.'

Cardinal Zen said it was unfortunate the arrests had been made, but that Hong Kong could learn from what had happened.

'I hope we learn from this particular event to avoid a certain culture which is much more pernicious than a single event,' he said. 'That is the culture of oppressing the weak, because these Korean people are very mild and kind.'

The Police Inspectors' Association greeted the cardinal's remarks yesterday with derision. Mr Lui questioned whether Cardinal Zen was in possession of the full facts of yesterday's court judgment.

'The cardinal must be in a good mood after his trip to the Vatican. He is obviously so busy that when he set foot on Hong Kong soil, he had no chance to read the transcript of the judgment. If he had, I don't think he would have come to such a conclusion,' said Mr Liu.

He said officers' morale had not been dented by the failure to prosecute anyone successfully over the riots, in which 64 officers were injured.

Peter Malanczuk, dean of law at City University, believed that the mass arrests and subsequent court proceedings had been necessary to convey that the rule of law was enforced rigorously in Hong Kong.

'Hong Kong is very much rule-of-law-oriented. It has to be made clear, not only to those who are citizens but those outside Hong Kong, that it follows procedure.

'This engenders trust in the legal system - it is the backbone of the financial markets,' Professor Malanczuk said.