Former surgeon Jayant Patel did not mean to kill or harm his patient Mervyn Morris.
But his decision to subject the 75-year-old to an ''inappropriate'' and ''unnecessary'' operation led to Mr Morris's death, Crown prosecutors contend.
Whether the prosecution is right or not is what 12 men and women in the Brisbane Supreme Court will have to decide in a few weeks.
Opening the case against Dr Patel, the prosecutor, Peter Davis, said there was no suggestion the former Bundaberg physician had intentionally set out to harm Mr Morris.
But Mr Davis said the prosecution believed Dr Patel misdiagnosed his patient's condition, and that his decision to operate amounted to criminal negligence.
''The accused performed some medical procedures on Mr Morris,'' Mr Davis said.
''The Crown case is that as a result of those medical procedures Mr Morris died. Even if the accused was doing his very best on Mr Morris but it was a criminal negligent best, then he is guilty of manslaughter.''
Mr Davis said the evidence pointed to Mr Morris suffering from proctitis, which can sometimes be the result of radiation treatment. It causes a lot of the symptoms, including rectal bleeding, that Mr Morris displayed at the Bundaberg Base Hospital in March 2003.
Mr Morris - who also had a weak heart, which Mr Davis said the prosecution's expert witnesses will say was just one reason he should not have been operated on - was diagnosed with prostate cancer in 1994 and treated with radiotherapy.
''Any reasonable doctor would obviously have noticed [that Mr Morris had proctitis],'' Mr Davis said.
But he said Dr Patel had missed that and instead decided to operate on Mr Morris to remove a piece of his colon, a decision the prosecution maintains was negligent.
''He never found the site of the bleeding,'' Mr Davis told the jury.
''The accused never worked out whether that bit that's now missing [from the colon] is where the bleeding was coming from.''
One week later, Dr Patel was forced to operate on Mr Morris for a second time, after Mr Morris suffered a complication that sometimes occurs in patients who have had abdominal surgery - an abdominal wound dehiscence, in which layers of the wound separate.
The prosecution contends that, without the first unnecessary surgery, the second operation would not have been required.
Mr Morris died on June 14, 2003.
The prosecution has accused Dr Patel of failure to ''take reasonable care and show reasonable skill'' and alleges that, as a consequence of failing in his legal obligation to show that care and skill, Mr Morris died, which equates to manslaughter.
The jury, made up of nine women and six men (including three alternates), was told by Mr Davis he would attempt to avoid causing them ''information overload'', as the case against Dr Patel was heavy with medical jargon and terms.
The jury members were handed medical dictionaries to help them understand some of the terms that will be repeatedly used throughout the case, by witnesses, the defence and the prosecution themselves.
The men and women had been selected on Wednesday following a rigorous polling process designed to test their ability to be impartial in the case. Mr Davis touched on the unusual process, telling the jury: ''I think we all know he was a surgeon at Bundaberg Base Hospital.''
Watching Mr Davis carefully, some taking notes, all the jury members seemed prepared to accept the challenge before them.
The trial, before Justice George Fryberg, continues.