By Brian Maass

DENVER (CBS4)– A series of emails appear to be the “smoking gun” in a controversy over the planned expansion of the Colorado Convention Center in Denver, according to multiple sources familiar with the growing scandal.

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Four sources familiar with the emails, but not authorized to speak publicly about them, say the documents clearly suggest collusion between Trammel Crow, the company managing the convention center expansion, and Mortenson Construction, a contractor bidding on the $233 million project. One source familiar with the emails told CBS4 they were “damning.”

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On Tuesday, Denver Mayor Michael Hancock announced a halt to the contractor selection process and said he was asking the Denver District Attorney to investigate.

CBS4 Investigator Brian Maass interviews Denver Mayor Michael Hancock (credit: CBS)

“And we saw some things that quite frankly concerned us that it was not fair and would lean toward certain players and competitors”, said Hancock.

Trammel Crow said Wednesday it fired an employee but declined to name the person.

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However, multiple sources told CBS4 the employee was Trammel Crow Senior Vice President of development management Mike Sullivan, 57, who has been with the company since 2006. Those same sources say Sullivan was exchanging emails with personnel from Mortenson and those emails suggest collusion between the two entities.

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CBS4 attempted to contact Sullivan via phone and email but received no response. His presence and past employment with Trammel Crow appeared to have been quickly scrubbed from the companies’ website. Earlier, online bios for Sullivan stated he is a civil engineer from the U.S. Military Academy and has had a more than 20-year career in construction management in Colorado.

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In a Thursday afternoon interview, Hancock said he was “dumbfounded” by the emails that underpin the case.

“The blatancy of what we saw and how brazen these people were to communicate the way they were, clearly violating the rules of competitive bidding … just blew me away,” said Hancock.

Denver Mayor Michael Hancock (credit: CBS)

Bill Mosher, Trammel Crow’s top executive in Denver, did not respond Thursday to multiple calls and emails from CBS4. On Wednesday, Mosher issued an apology for what had happened.

Maja Rosenquist, a Senior Vice President at Mortenson, said in a statement the company had received a letter from the City and County of Denver regarding the bidding process.

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“We take the issues raised by the City very seriously and are committed to addressing this matter thoroughly and appropriately. 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,” said Rosenquist.

The convention center expansion and its funding were approved by Denver voters in 2015. The expansion will add meeting and ballroom space along with a massive outdoor terrace. Technology improvements are also part of the upgrades.

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Hancock said the city was ending its contract with Trammel Crow and will restart the process to identify a design/build contractor with a new selection panel.

“Make no mistake about it when this sort of thing happens taxpayers lose,” said the Mayor. “This is going to be a costly process to stop and start over – it costs money and we are going to do everything to make sure taxpayers are made whole.”

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He added he was offended by anyone tweaking the process and putting minority and female contractors at a disadvantage.

Denver City Attorney Kristin Bronson told CBS4 the city is attempting “to quantify its damages” incurred during the bidding process. Bronson said her office was attempting to hire an outside attorney to help “recoup these losses from those responsible.”

The rooftop terrace at the Colorado Convention Center (credit: City of Denver)

Bronson said she could not provide any estimates for how much the aborted bidding process may have cost Denver taxpayers.

Carolyn Tyler, a spokesperson for the Denver District Attorney’s office, told CBS4 ,”We are still in the document review phase” and no decision has been made yet on whether to open a full criminal investigation.

CBS4 Investigator Brian Maass has been with the station more than 30 years uncovering waste, fraud and corruption. Follow him on Twitter @Briancbs4.