The auditor’s office wants to investigate money that was spent on the plant and current plans for the proposed facility.

Denver Zoo announced in September it would discontinue, a least temporarily, plans for a $3.7 million biomass gasification system that turns animal waste into energy. Zoo officials say if the plant is built, it will not be on zoo grounds.

“The Zoo’s obstruction has increased the perceived risk to the City involved in this contract,” O’Brien said. “We have to wonder, what is it that the Zoo doesn’t want us to discover?”