Colorado Secretary of State Wayne Williams is investigating reports that votes have been cast for people months or years after their deaths.
A review of databases by KCNC-TV of voting histories in Colorado compared with federal death records turned up dozens of discrepancies.
The discrepancies involve mail ballot votes that were cast and possible errors by election judges.
Williams says Colorado's election system is not perfect and there are gaps that allow situations like this to occur.
"We do believe there were several instances of potential vote fraud that occurred," Williams said.
According to KCNC-TV, a woman from Colorado Springs died on Oct. 14, 2009.Colorado voting records showed ballots cast for the woman in 2010, 2011, 2012 and 2013. Her husband died on Sept. 26, 2008, and votes were cast in his name the following year.
In Denver, a World War II veteran who died Dec. 13, 2004, had votes cast in his name at a polling place two years later.
Voting for another person is illegal and district attorneys are also investigating.
El Paso County Clerk and Recorder Chuck Broerman said he was shocked by the findings.
"This cannot happen," he said. "We cannot have this here or anyplace in our country. Our democracy depends on it. People have spilled their blood for the values and underpinnings and beliefs of this country."
Broerman said the man and woman remained on active voter rolls and mail ballots were still sent to their home because there was no way to delete their names from eligible voter rolls.
State voting officials say they can only delete names from voting rolls if death databases have the correct name, dates of birth and addresses. Even minor errors require further scrutiny, which can lead to potential fraud and mistaken votes.
Officials say about 2 million votes were cast in Colorado's last election cycle and 8,000 ballots were rejected because signatures did not match.