Assistant Commissioner John Lee said only three people were involved - - the two patrolling constables and off- duty officer, Tsui Po-ko, who was attached to the North Lantau division.

Shortly after 1am last Friday, Tsui and uniformed officers Tsang Kwok- hang, 33, and Sin Kar-keung, 28, were found slumped close to each other in the blood-splattered subway at the junction of Canton and Austin roads.

Tsui and Tsang were pronounced dead at Queen Elizabeth Hospital, while Sin, who was critically wounded, had his condition changed from serious to stable Monday. But, police would not say if he had given a statement on the shooting.

Lee told a press conference investigators believe that Tsui had ambushed the two constables in a bid to rob them. "He was targeting their firearms and ammunition," he said.

Tsui, he said, had no history of mental illness. The police are seeking outside help to try to better understand what Tsui might have been thinking at the time and why he wanted the guns.

What is known is that a total of 10 shots were fired by all three men, but Lee was unsure about who fired which shots. Without naming names, he said: "The suspect had five wounds, we think the shots were fired by one of the officers."

Lee said Tsui died from wounds to the vital organs - the heart and lungs.

A police source said Tsui had started the exchange when he wounded Sin who returned two shots, but missed.

Tsang hit Tsui with five shots to his torso. The sequence is unclear but, the source said, at some point, Tsui shot Tsang in the face. The wound did not kill Tsang instantly which allowed him to put his gun back into its holster and alert other officers before he choked to death on his own blood.

Contrary to media speculation, Lee said there is no knowledge of any relationship or a bitter past between Tsui and the other two officers involved in the shooting.

Nor did Tsui know Leung Shing- yan, the officer who was shot to death five years ago outside a Tsuen Wan flat when he went there to investigate a noise complaint, and from whom the revolver used by Tsui was stolen.

The same gun was used to rob a branch of Hang Seng Bank on Castle Peak Road, Tsuen Wan, in December 2001 during which a masked man shot and killed a Pakistani security guard before escaping with about HK$500,000.

Although police sources have said about HK$2.1 million had been found in Tsui's workplace locker and at his home in Tung Chung, Lee said the missing robbery loot had yet to be recovered.

But he said it is believed Tsui was holding Leung's gun when his body was found in the subway.

He said the revolver seized at the scene of gunbattle was very rusty and stressed that investigations would have to continue before further conclusions could be drawn. "At this stage, we cannot draw definite conclusions about its connection, ballistically, to the two cases," he said.

Lee said as there may be an inquiry into the deaths, he could not reveal too many details of the investigation.

But he emphasized there was nothing at this stage to show that Tsui was linked to triads or organized crime.

"Gambling and other things are among the many areas the [ Organised Crime and Triad Bureau] is looking into," Lee added.

He described the shoot-out as exceptional. "In my 29 years of service, this is the first case involving a suspect like this. So, this is a very individual case."