It was 29 minutes past midnight when two junior police officers entered the backyard of a Sefton home. They had been told to wait while their colleagues at the front of the house were getting ready to move in with police dogs to restrain an agitated 25-year-old Vietnamese student.

But within 40 seconds Thinh Ba Le had been shot with a stun gun and handcuffed. Minutes later he was dead.

Unlike the death of a Brazilian student in Sydney this month, which received global coverage, Mr Le's death in October 2010 went largely unreported.

The coroner found police had acted ''very well'' when they were suddenly confronted by Mr Le holding two knives rushing towards them, but the court heard the role the Taser played in his death was unclear. The case, like recent tragic deaths, raises issues about the safety of the stun gun and police investigations into critical incidents.

The inquest heard instructions for the two officers to be separated were not followed, but there was no evidence they had colluded or discussed their evidence.

State Coroner Mary Jerram said she would write to Police Commissioner Andrew Scipione suggesting better training in the handling of critical incidents.

The guidelines were important, she said, and were designed to ''keep the evidence uncontaminated because when police are separated immediately after such an incident with no chance to speak to each other … their evidence is given greater credibility''. This was also designed to protect police, she said.

The inquest into Mr Le's death also heard he was stunned in the chest - despite a safety warning from the manufacturer a year earlier.

He was hit with one of its barbs in the lower abdomen, but another was imbedded in the left of his chest, centimetres from his heart.

In October 2009, Taser International warned police forces worldwide that ''to increase the safety margin'' the stun-guns should not be aimed at the chest, to avoid the ''remote risk'' of a heart attack.

Constable Paul Morrison, who fired the stun gun, said he had not been trained to avoid hitting the upper chest or aim for the lower abdomen. He told the inquest late last year that he had been trained to avoid the face and abdomen and knew aiming for the back was best, but otherwise believed it was acceptable to hit the ''centre mass''. He said he had aimed the Taser's red dot just below the sternum.

Counsel assisting the inquest Robert Ranken said ''there ought to be some specific instruction by NSW police to officers who are trained in the use of Tasers as to not just what the preferred target areas are, but also why they are''.

The Melbourne forensic physician Morris Odell said there was ''a slight possibility that the shock from a Taser could induce or contribute to a disturbance of heart rhythm''.

The likelihood depended on the location of the darts, the strength of the Taser's electric pulse, the presence of stimulating substances, such as the drug ice, in the target's body, and any cardiac conditions.

Mr Le had been drinking heavily in the hours before the incident. He also had traces of heroin in his blood, but neither are stimulants, Dr Odell said. Suggestions he had a heart problem were not substantiated and the autopsy found no evidence of any heart problems.

The cause of his death could not be established at autopsy, but efforts to resuscitate him were hampered when Mr Le vomited and food became lodged in his airways.

Dr Istvan Szentmariay, who conducted the autopsy, told the court: ''Don't forget that Taser-associated deaths are not necessarily caused by [the] Taser itself.''

After being stunned, Mr Le hit the ground, chest first, he screamed and made gurgling noises. Initially he was fine but within five minutes he was unconscious and barely breathing. His eyes were bulging and he soon received CPR. When the first ambulance arrived at 42 minutes past midnight, Mr Le was dead.

Me Le had only lived in Sydney for seven months, and was studying English and planning to enrol at university.

Police had been called to the Sefton home of his former girlfriend after she complained he had assaulted her. She fled to a neighbour's house and Mr Le allegedly banged on the door and yelled threats.

''I am satisfied that there was completely appropriate behaviour by all police officers involved,'' the coroner found.