Mayor Michael Hancock has halted the search for a contractor to run the $223 million Colorado Convention Center expansion after the bidding process was allegedly undermined, according to a statement released Tuesday.

The administration terminated its contract with Trammel Crow, which is overseeing the ostensibly competitive contracting process. The city attorney’s office found evidence that city documents were released improperly, “improper” discussions took place, and that approved project plans were altered, according to the statement.

“We believe this is a significant breach of the public trust and a willful violation of a competitive bidding process,” Hancock said in a press release. “We will never tolerate this type of behavior from our contractors and will continue to address this swiftly and aggressively.”

Hancock has asked the Denver Office of the District Attorney to investigate.