QUEBECKERS were outraged in 2010 when Maclean’s, a Canadian magazine, labelled their province the most corrupt in the country. True, a Quebec-based scandal had helped to topple the federal government in 2006, and evidence was mounting of bid-rigging and kickbacks in local administrations. But Quebec’s defenders claimed that the revelations simply showed their anti-corruption investigators were more vigilant than others. Months of damaging testimony to a corruption inquiry have now left even the province’s boosters short of excuses.

The inquiry, headed by France Charbonneau, a justice of the Quebec Superior Court, has this month led to the resignations of Gérald Tremblay, the mayor of Montreal, and Gilles Vaillancourt, mayor of neighbouring Laval. Both still vehemently maintain their innocence, yet had little choice but to go.

Mr Tremblay has not been accused of personal involvement in the kickback scheme—described at the inquiry by two former Montreal engineers—in which the value of construction contracts was fraudulently inflated. The firms involved, some of which are said to have links to the mafia, allegedly gave back some of their remuneration to municipal employees, and made generous donations to political parties. But the racket took place on Mr Tremblay’s watch. Martin Dumont, a former organiser for his Union Montréal party, testified that the mayor knew the party kept two sets of books, separating clean and dirty money, but chose to turn a blind eye. Mr Tremblay denies any such knowledge.

Meanwhile Mr Vaillancourt took sick leave and then resigned after anti-corruption police raided his offices. A construction boss told the inquiry that firms were expected to hand over 2.5% of every contract they received in Laval to the mayor. He, too, denies the allegation.

Other heads have already rolled. Four further Montreal employees have been suspended without pay pending further investigations. The mayor of Mascouche and the former mayor of Boisbriand, two smaller cities north of Montreal, were charged with fraud before the inquiry began. And more may yet follow: Ms Charbonneau is due to submit her report in October 2013.

Although the inquiry’s mandate is restricted to Quebec, the testimony has also pointed to possible wrongdoing at the federal level and in the neighbouring province of Ontario. Assorted criminologists and police officers have testified about the mafia’s sway in Ontario. One theory suggests that the mob there is just as powerful as in Quebec, but is less rancorous than its counterpart and so attracts less attention (as it happens Joseph di Maulo, an alleged kingpin, was shot dead on November 4th in the driveway of his Quebec home). Politicians elsewhere don’t seem overly concerned by these insinuations.

None of this means that Canada, which Transparency International, an advocacy group, rated among the world’s cleanest countries in its 2011 index of perceptions of corruption, has suddenly become Nigeria. But the episode does suggest that it can no longer be complacent about graft.