Police sources say they found marijuana in his system after the collapse and he also admitted to taking codeine and other prescription drugs. Authorities added that he was outfitted with a soft cast up to his elbow.
Sources told ABC News that the operator knocked down a wall, causing the four-story structure to topple on Philadelphia's busy Market Street Wednesday morning, killing a total of six people.
Meantime, the tragedy is bringing mounting fallout in a city where demolition contractors are lightly regulated.
Just one day after the tragedy, officials began inspecting hundreds of demolition sites across the city, the first of what could be several lawsuits was filed, and a criminal investigation appeared to be in the works as rescuers ended their search through the rubble for survivors and victims.
The chief of the district attorney's homicide unit and a veteran homicide prosecutor were spotted amid the building debris.
A lawsuit filed late Thursday seeks financial damages on behalf of Nadine White, who was buried in rubble but survived.
"This is the most egregious construction accident I think I've ever been involved in," said White's attorney, Robert Mongeluzzi, who says demolition contractor Griffin Campbell violated several federal safety regulations, while building owner Richard Basciano should have picked a more qualified and competent contractor to do the work.
Mongeluzzi has asked a Philadelphia judge for an emergency order to allow him to access and inspect the collapse site. A ruling could be issued as early as Friday.
Meanwhile, the city has started inspecting hundreds of demolition sites in the wake of the collapse. By Thursday afternoon, inspectors had visited about 30 out of 300 open demolition sites and planned to get to the rest by next week.
The spot inspections included all four construction and demolition sites connected to Campbell. The city found violations at two sites and ordered a halt to the work.
Campbell has been arrested on charges involving drugs, assault and insurance fraud and has had two bankruptcy filings. His daughter, Dominique Lee, who answered the door at his home, said he wasn't there but was "mourning the loss of those people just like everyone else."
Councilman James Kenney and others are calling for a review of the city's demolition application and inspection process. The city does check the condition of buildings to be torn down before demolition can begin - and inspects them again after the tear-down is finished - but does not require an inspection during demolition.
A pre-demolition inspection at the site on May 14 turned up no issues, said Carlton Williams, head of the city's Department of Licenses and Inspections.
The mayor's office identified the six victims as Anne Bryan, Roseline Conteh, Borbor Davis, Kimberly Finnegan, Juanita Harmin and Mary Simpson.
The Associated Press contributed to this report.
