He said the circumstantial evidence only suggested Tsui could have been involved in the three shooting incidents but it was difficult to determine the extent of his involvement and whether anyone else was involved.

Solicitor Daniel Wong Kwok-tung, representing Tsui's wife, Li Po-ling, said the family was unable to hire any expert to say Tsui had no personality or mental problems.

He said Tsui was unfairly described as a rogue and a demon by the media, and only the dark side of the constable's personality had been recalled by witnesses who used to be his friends.

'It's very easy to make allegations against Tsui, but it's very difficult to derive how much he was involved in those killings,' Mr Wong said.

Representing Tsui's mother, Cheung Wai-mei, barrister Arthur Yip Chi-ho said the evidence was not sufficient to prove Tsui killed Constable Leung Shing-yan, who was shot dead on March 14, 2001, and security guard Khan Zafar Iqbal, who died in a bank robbery on December 5, 2001.

'DNA tests revealed Tsui could have been at the death scene but did not help us to infer who killed Leung,' he said.

'It had been five years from 2001 when the stolen revolver of Leung was recovered in last year's shootout in which Tsui died. No one could tell if the revolver had been handled by someone else.'

Regarding the bank robbery, Mr Yip argued the indirect evidence produced - including a pair of Mizuno running shoes, a red polo shirt and a balaclava - suggested only that Tsui had possessed similar attire to the robber. 'Even though Tsui was believed to have had a suspicious sum of more than HK$500,000, there was no direct evidence to identify Tsui as the robber who entered the bank.'

Mr Yip also raised doubts about evidence relating to the Tsim Sha Tsui shootout on March 17 last year.

Coroner Michael Chan Pik-kiu will sum up the case to the jury on Monday before they start deliberations.