The bidding process for the $233M expansion of the Colorado Convention Center came to a sudden halt recently amid charges of collusion between Trammell Crow Co., which was overseeing the process, and Mortenson Construction, a bidder.

Specifically, the city alleges that there was an improper release of city documents to the contractor and improper discussions about the bidding process between the two companies.

A series of emails appears to be the smoking gun suggesting collusion between Trammel Crow and Mortenson, CBS Denver reports, citing four anonymous sources.

CBS also reported, citing multiple sources, that Trammel Crow fired Senior Vice President of Development Management Mike Sullivan, who had been exchanging emails with Mortenson personnel.

Denver Mayor Michael Hancock has put the selection of a contractor for the project on hold, and the city has terminated its contract with Trammell Crow, which was being paid $9M to oversee the process.

The city has also asked the Denver District Attorney’s office to investigate. As yet, DA Beth McCann hasn't announced her plans.

“We are mortified that this occurred,” Trammell Crow Senior Managing Director Bill Mosher, in the Denver office, said in a statement.

“In no way were the actions of the employee authorized by Trammell Crow Company," Mosher said. "They are contrary to the values of our company and our longstanding business practices. We are cooperating fully with the City of Denver and continuing to conduct our own internal investigation.”

"We take the issues raised by the City very seriously and are committed to addressing this matter thoroughly and appropriately," Mortenson Senior Vice President Maja Rosenquist said in a statement, Engineering News-Record reports.

"We are conducting our own review of our participation in the RFP process and will cooperate with any further inquiries by the City or the District Attorney’s Office,” Rosenquist said.

Hensel Phelps Construction, PCL Construction and Mortenson were the three finalists for the contract. The city’s executive director of public works is requesting a review of Mortenson’s prequalification status for bidding on future projects, Engineering News-Record reports.

The Colorado Convention Center expansion, which was approved by voters in 2015, will include the development of as much as 185K SF of new meeting, ballroom and other space, along with a 50K SF outdoor terrace on the roof of the existing center.