Discredited pathologist Dr. Charles Smith jumped to "ridiculous" conclusions in a number of child death cases he oversaw as director of the province's forensic pediatric pathology unit, a pathologist who frequently clashed with Smith told a public inquiry Tuesday.

Dr. Ernest Cutz, an expert in sudden infant death syndrome or SIDS, said there were a number of cases where Smith suspected criminal activity even though there was no evidence to support his opinions.

One case involved a small child who had the croup and died after collapsing in a shower that was intended to alleviate his respiratory problems, Cutz said.

During the autopsy, Cutz found a fungal obstruction in the child's airway, which he concluded had developed as part of his illness, dislodged and caused the child's death.

But Smith thought the obstruction was a red herring — something that happened while the child was being resuscitated — and suspected the child's mother had a mental disorder and was somehow responsible for the child's death, Cutz said.

In another case, Cutz concluded that an infant, found tangled in the cord from a venetian blind close to the crib, had died accidentally. But Smith said the incident "looked suspicious" and that the parents might be involved, Cutz said.

"I found it quite ridiculous, especially knowing that this is a recognized hazard, which has been documented in the literature, and it has even been the subject of television reporting," he said.

There was no evidence to support Smith's opinion, and he never explained the reasons behind his suspicions, Cutz added.

"There was no evidence from police or other investigations that anything untowards has happened, and I presume that's how it ended up classified," he said.

The inquiry into pediatric forensic pathology in Ontario also heard about Cutz's misgivings about the unit's protocols — particularly its "think dirty" protocol — which he felt had strayed from its initial academic focus to forensics.

Cutz, who researched SIDS with world-renowned expert Dr. Laurence Becker prior to the unit's formation in 1991, said they had supported the move to form the unit because they believed it would help fund and support their research.

But their work effectively stopped when they were cut off from accessing tissue samples from SIDS cases investigated by the coroner.

Cutz also said he had concerns when Smith was appointed director of the unit.

"I didn't know if Dr. Smith was qualified, but I didn't think that he had the appropriate training to assume that, to do those kinds of (forensic) cases," Cutz said.

"But it was his choice.… I wouldn't have recommended him to do it."

The inquiry is investigating the deaths of 20 children which involved criminal proceedings where Smith was a forensic pathologist. Led by Justice Stephen Goudge, the inquiry was prompted by a review of 45 cases Smith handled between 1991 and 2001.