Testimony at Quebec's corruption inquiry was challenged on Wednesday, as lawyers spent a second day cross-examining headline-grabbing witness and former construction boss Lino Zambito.

A lawyer for the City of Montreal challenged the star witness to explain memory gaps and tried to seek inconsistencies in his story.

City lawyer Martin St-Jean questioned Zambito on specifics about a city contract Zambito said former city manager Robert Abdallah tampered with through an intermediary, an engineer overseeing the work.

Zambito, former co-owner and vice-president of now-defunct Infrabec Construction, said that he never met directly with Abdallah or discussed the matter with him and he doesn't know whether cash he paid as part of an alleged kickback scheme was ever actually turned over to Abdallah.

"There was an engineer who was representing the city who told me that the contract would be authorized if I bought... extra piping," Zambito insisted, when asked about his company's work on the $10-million sewer contract in east-end Montreal in 2005.

"I told you what was reported to me by the engineer who is representing the city who is in contact with Mr. Abdallah."

Short on specifics

A number of city employees and the Montreal mayor's political party were accused by Zambito of taking kickbacks on contracts. But the ex-construction boss has occasionally come up short when pressed for specifics.

For example, Zambito could not put a dollar figure on the three per cent cut of city contracts that he allegedly paid to Mayor Gérald Tremblay's Union Montréal party through a middleman, Mafia associate Nicolo Milioto.

On the subject of local engineers and planners who were allegedly on the take, the city lawyer questioned Zambito about the numbers and amounts paid. This was after Zambito had stated an engineer claimed a cut of contingency payments to his company for excess costs, while another took one per cent of the value of rigged contracts.

Zambito said the practice was discussed among contractors and, although he never saw anyone else pay, he insisted he paid in cash. He said the exchanges took place in various locations around town, without witnesses.

"It was the rule," Zambito said.

Zambito couldn't say how many times he'd worked with different city employees that he'd named.

Lawyer St-Jean expressed frustration that the reputation of city employees had been tarnished while Zambito couldn't provide more specific information.

"It's easy to throw names out there but, at some point, you have to come back with solid details," St-Jean told Zambito.

The commission chair appeared to defend the witness.

"In an inquiry, you have to start somewhere and the evidence will come gradually over time," France Charbonneau said.

Finishes testifying

In the early moments of his eight days of testimony, Zambito explained that certain construction companies, including his own, operated as a cartel.

He testified that these companies colluded to drive up the cost of public contracts, with a 2.5 per cent commission going to the Italian Mafia on rigged bids.

He has also said that, in 2005, he began paying the equivalent of three per cent in kickbacks to the ruling political party in Montreal. Over a longer period, he said he was paying additional bribes to city engineers and bureaucrats.

He has also said that he's heard that a 2.5 per cent cut of contracts in Laval, north of Montreal, went directly to that city's mayor, but he never paid that amount himself.

Zambito has also admitted to illegally funding political parties at the provincial level. The inquiry says it will not explore whether such wrongdoing occurred at the federal level.

None of Zambito's allegations have been proven in court.

He started testifying Sept. 27 and completed cross-examination on Wednesday afternoon.

With files from CBC News