A pathologist had a "slapdash" approach to evidence in the case of Sally Clark, a GMC hearing has heard.
Dr Alan Williams denies professional misconduct
Mrs Clark was convicted of murdering her two baby sons in 1999, but was freed on appeal in 2003.
The General Medical Council heard Dr Alan Williams did not disclose key test results at her original trial.
Dr Williams, aged 58 and based in Macclesfield, Cheshire, denies serious professional misconduct. The case continues.
Mrs Clark had always denied smothering her first son, Christopher, when he was 11 weeks in December 1996 and shaking her second baby Harry to death in January 1998 when he was eight weeks old.
Dr Williams carried out post mortems on both of Mrs Clark's sons after their deaths.
At first he said Christopher had died from a lung infection but changed his mind, after Harry's death, and claimed he was smothered.
The GMC hearing heard Dr Williams told Mrs Clark's 1999 murder trial that Harry appeared to have been shaken to death but he did not keep proper records of tests he carried out, throwing doubt on the quality of his work.
However, the appeal in 2003 that cleared Mrs Clark was told by prosecutors that Dr Williams was aware of microbiological tests which had shown that Harry had the bacteria staphylococcus aureus in his body, which was the most likely cause of death - but that he did not reveal this at her trial.
Tests 'not carried out'
Roger Henderson QC told the GMC's professional conduct committee in central London: "Here was a baby (Harry) who had died in circumstances which we would suggest called for the most meticulous of examination.
"His elder brother had died. Dr Williams knew this. It will be our evidence that the absence of a contemporaneous report of the ribs and the absence of any photographic record shows he had a slapdash approach.
Sally Clark was freed in January 2003
"It may have been expected from a forensic pathologist that his findings might be the subject of an intense scrutiny and he would have to answer to his findings potentially in a coroner's court or a criminal court.
"As a matter of routine, Dr Williams should have been meticulous in his work."
Mr Henderson is representing former Tatton MP Martin Bell, who made an official complaint against Dr Williams. Mr Bell was Mrs Clark's MP at the time of her conviction.
The QC alleged Dr Williams was "incompetent" in his consideration of treatment of Harry's eyes, spinal cord and ribs.
He said the post mortems on both children were of a standard which impaired the reliable evaluation of evidence of the cause of death, it was alleged.
Mr Henderson said: "There are grave problems caused by Dr Williams' lack of meticulous detail."
He said: "Justice demands that the best evidence be available in order to permit the testing of the best evidence of both Crown and the defendant and for consideration by a coroner, a judge and jury."
He argued that if a rib had been dislocated, there may have been damage and bleeding which could be identified by taking "suitable" samples.
"There is no contemporaneous record to suggest that such sampling occurred," he said.
Dr Williams denies serious professional misconduct.
Earlier, James Turner, QC for Dr Williams, called for the case to be thrown out or adjourned, arguing there had been a "scandalous delay" in bringing it.