Local officials in Colorado acknowledged "very serious" voter fraud after learning of votes cast in multiple elections under the named of recently-deceased residents.

A local media outlet uncovered the fraud by comparing voting history databases in the state with federal government death records. "Somebody was able to cast a vote that was not theirs to cast," El Paso County Clerk and Recorder Chuck Broerman told CBS4 while discussing what he called a "very serious" pattern of people mailing in ballots on behalf of the dead.

It's not clear how many fraudulent ballots have been submitted in recent years. CBS4 reported that it "found multiple cases" of dead people voting around the state, revelations that have provoked state criminal investigations.

"We do believe there were several instances of potential vote fraud that occurred," said Colorado Secretary of State Wayne Williams. "It shows there is the potential for fraud."

Colorado is a perennial battleground state in presidential battleground states. President Obama beat Republican nominee Mitt Romney by 51-46 in 2012. Clinton leads Trump by 2.5 points in the RealClearPolitics polling average, although there is wide variance in the three most recent surveys. One shows Trump leading by four, another shows them tied, and the third shows Clinton up nine points.

Williams plans to pursue criminal charges in the incidents uncovered by CBS4, such as the case of an El Paso County woman who died in 2009 but had ballots cast in her name in 2011, 2012, 2013, and 2014. It's difficult to prove that any particular person committed the fraud, however. "If our laws are not strong enough to prosecute this case, I don't know what can be prosecuted," Broerman told the Denver Post.

Voter fraud is a perpetual concern among Republican politicians, often scoffed at by Democrats. Some studies show that it is not a widespread problem, but certain high-profile incidences have kept the concern alive on the right.

It's not clear how many fraudulent ballots have been submitted in recent years. CBS4 reported that it "found multiple cases" of dead people voting around the state, revelations that have provoked state criminal investigations. The Milwaukee (Wis.) Police Department reported in 2008 that there was an "illegal organized attempt to influence the outcome of [the 2004] election in the state of Wisconsin." There were more votes counted than the number of voters who officially cast ballots, according to the report — about 5,000 more, in a presidential battleground decided by 12,000 votes.

El Paso County officials found 78 deceased people on their voter rolls after the CBS4 report was published, according to the Post, but they have previously removed 448 people from the registered voter list since 2012.

Williams suggested that the system would be more effective if state lawmakers give the secretary of State's office more discretion in deciding that the name of someone who died matches the name of someone listed as an active voter.

"Our office is working to ensure all such incidents are prosecuted and that laws and rules are adjusted to make vote fraud as difficult as possible," he told the Post. "[D]oes it make sense to broaden criteria to allow us to make a decision even if the name may be different?"