No criminal investigation is planned after a worker at a federal laboratory in Colorado was accused of intentionally manipulating test results, which could taint research on energy and toxic chemicals.

Officials said Tuesday that opening a criminal investigation would require an additional review by the Interior Department, which oversees the lab. They said they have no plans to do that because the employee no longer works there.

It wasn't clear if the employee resigned or was fired. His name hasn't been released.

The Interior Department reported last month the manipulation occurred at a lab in the Denver suburb of Lakewood. The falsified data may have affected 24 projects costing a combined $108 million.

Officials said they weren't sure why the employee manipulated the results but said it wasn't for personal gain.