Commission lawyers accused him of "distancing" himself from the building, which the hearing had been told suffered several serious construction issues.
Since giving evidence, he has been accused of stealing the identity of a British engineer he once worked with in South Africa and faking an engineering degree to get jobs in New Zealand and Australia.
The fake degree from Sheffield University meant he was able to gain entry to a masters program at University of NSW in 1971, which led to him getting a Masters of Engineering Science in highway engineering in April 1974.
University of NSW has launched an internal investigation into Shirtcliff's background, and has said if the claims were proved correct the institution would cancel his degree.
Australia's professional body for the engineering industry has also launched a probe into the "very serious" allegations, especially given Shirtcliff had been working for engineering consultancies.
A spokeswoman for Engineers Australia said if it concluded Shirtcliff made up his engineering qualifications, it would call in police.
"Engineers Australia is in the final stages of completing our investigation regarding the allegations appearing in the media concerning a man named William Anthony Fisher," the spokeswoman told APNZ.
Membership would be cancelled for anyone misrepresenting qualifications, she said, but added they would go further if necessary.
"If our inquiries suggest that a crime may have been committed, then we will refer the matter to the Australian Federal Police," she said.
Shirtcliff, who now lives in a plush Brisbane home, drives a luxury car and owns expensive launch, denies the claims.
His Brisbane lawyer David Tucker has issued a statement saying: "Our client, Will Fisher, strenuously denies all of the allegations.
"We are instructed that the allegations of identity theft are untrue and without any substance whatsoever."
He said Shirtcliff was unavailable for comment and was "quite distressed by the unwarranted attack" on his integrity.
Families of CTV victims say Shirtcliff has committed perjury by lying about his engineering qualifications to the Canterbury Earthquakes Royal Commission.
They have called for the inquiry to reconsider his evidence.
But the royal commission has issued a statement saying the hearing into the CTV Building collapse is complete and it is satisfied construction issues had been "well canvassed".
Commissioners have retired to consider their findings before delivering their final report by November 12.