ELEANOR HALL: The chief police investigator looking into the death of an Aboriginal teenager, whose fatal accident led to a riot in the suburb of Redfern, has acknowledged there are "unexplained inconsistencies" in the evidence of a key police witness in the case.

There have been allegations police were chasing 17-year-old Thomas "TJ" Hickey in the moments before he suffered fatal injuries in a bicycle accident. Yesterday the Coroner allowed a key police witness not to give evidence because it could expose him to disciplinary action by the Police Commissioner. This morning, the inconsistencies in that officer's evidence were outlined to the court, as Michael Vincent reports.

MICHAEL VINCENT: Unable to question Senior Constable Michael Hollingsworth about his evidence, the Counsel assisting the Coroner, Elizabeth Fullerton SC, called on the investigating police officer to be recalled to the stand. She took him through Mr Hollingworth's statement, recorded interview and a video re-enactment of events.

It was put to Detective Senior Constable Michael Kyneur that in the three versions there were "unexplained inconsistencies". He agreed.

They were when Constable Hollingsworth first saw Thomas Hickey on his bike and more critically, when he last saw him riding and where his police car was at that point.

It's already been established that Constable Hollingsworth and three other police officers discussed these issues before writing their formal statements, on the day of the accident.

The video re-enactment, which was filmed a week after the accident, shows Constable Hollingsworth following a footpath Thomas Hickey took - evidence he didn't include in his original statement.

Constable Hollingsworth was in the public gallery when the video re-enactment was played this morning, but he left the courtroom at the point he began explaining Thomas Hickey's condition at the accident scene, where the teenager had been impaled on a fence.

On the video the officer described the scene as horrific - that the 17-year-old wouldn't stop moving and the blood was coming out fast, despite Hollingsworth's attempts to plug the wounds with rubber gloves.

Constable Hollingsworth said he kept looking at TJ Hickey's eyes to make sure he didn't pass out and that the teenager keep saying "don't let me die, don't let me die. I want my mummy."

Constable Hollingsworth has been excused from being a witness at the inquest because of the risk he could face disciplinary action by the Police Commissioner.

The family and supporters of Thomas Hickey were visibly upset by that decision.

The Coroner John Abernethy has directed the media to report that no inference adverse to Senior Constable Hollingsworth could be drawn from his refusal to give evidence in the inquest.

And Pauline Wright from the New South Wales Law Society says the public needs to remember that an inquest is not a trial.

PAULINE WRIGHT: Under Section 33 of the Coroners Act, and there are similar provisions in other acts for other courts, people are not obliged to give evidence if that evidence is going to tend to incriminate them and that can be whether it's in a criminal court or whether it might be a civil type of penalty that they might be facing if they give that evidence.

MICHAEL VINCENT: Because in this case, he's not facing any criminal charges or potentially and the only inference was that there was a risk he could face disciplinary action from the Police Commissioner.

PAULINE WRIGHT: I guess that was considered to be equivalent to a civil penalty because if he faces disciplinary procedures then he could be, the civil penalty he could face would, I guess, be dismissal from the police force, and that's probably the Coroner acting on his discretion under that section of the Coroners Act would be holding that it would tend to incriminate him in that sense.

MICHAEL VINCENT: Can you understand frustration at a key witness not giving evidence in an inquest, in a coronial inquest?

PAULINE WRIGHT: Of course, because everybody wants to know all the facts surrounding it and if one person is excused or can't be compelled to give evidence because it tends to incriminate them, then yes, it's going to be frustrating for those who want to know absolutely everything. But that is the rule that applies across all courts.

ELEANOR HALL: Chair of the Criminal Law Committee of the New South Wales Law Society, Pauline Wright, speaking there to Michael Vincent.