KANSAS CITY, Kan. — Some of the "handful" of noncitizens who made it onto voter registration rolls in Kansas in the last 20 years were registered because of confusion over the regulations or administrative errors, a national expert on voter fraud testified Friday in the fourth day of a trial that has grown increasingly tense.

Lorraine Minnite, a professor of political science at Rutgers University, testified in a trial that could determine whether thousands of Kansas residents are allowed to vote. The American Civil Liberties Union is challenging a 2013 Kansas law that requires people registering to vote to show documents — such as passports or birth certificates — to prove they are U.S. citizens. The law was championed by Kansas Secretary of State Kris Kobach, who is defending himself in the trial.

The ACLU contends the law has prevented thousands of people, mostly the young, elderly or poor, from voting in Kansas. Supporters argue the documentation requirement has prevented perhaps as many an 18,000 noncitizens from voting.

Minnite, author of "The Myth of Voter Fraud," said while doing research, she found discussion of voter fraud in Kansas "rocketed up" after Kobach began campaigning for Secretary of State in 2010. Kobach's continued public argument that voter fraud, particularly voting by noncitizens, is pervasive in the U.S. is "agenda setting" and not supported by her years of research, she testified.

During testimony on a Sedgwick County election spreadsheet that found 38 questionable voters, Minnite said several appeared to be on the rolls because of confusion or errors.

"That is normal, that happens everywhere," Minnite said. "It is not a freak thing that there might be errors in Kansas."

Garrett Roe, an attorney on Kobach's team, sparred with Minnite over whether it was necessary to determine intent to prove a crime had occurred. She said noncitizens who vote have committed an illegal act but are not necessarily guilty of fraud if they had no intention to deceive.

Later Friday, Kobach called a senior fellow at the Heritage Foundation, who also has written a book on voter fraud, to testify in support of the law.

The Kansas City Star reported Hans von Spakovsky testified that other methods of identifying noncitizen voters, such as matching legal immigrants' driver's licenses with voter rolls, would not be able to identify people living in the country illegally. He also said non-citizens aren't deterred by the possibility of prosecution for voter fraud "because we basically have an honor system" in U.S. elections.

Von Spakovsky served with Kobach on President Donald Trump's now-disbanded commission on voter fraud and worked for the U.S. Department of Justice with Kobach during President George W. Bush's first term.

Attorneys from the ACLU and the Kansas City-based Dentons law firm, which are representing voters suing Kobach's office, questioned von Spakovsky about an email he wrote in early 2017 expressing concerns about Trump's decision to put Democrats or mainstream Republicans on the voter fraud commission.

"There isn't a single Democratic official that will do anything other than obstruct any investigation of voter fraud," von Spakovsky wrote in the email.

Von Spakovsky testified that even a small number of non-citizens on voter rolls "could make the difference in a race that's decided by a small number of votes," but during cross-examination acknowledged that he could not name a specific federal election that was decided by non-citizen votes.

Throughout the week, U.S. District Judge Julie Robinson has stopped testimony to admonish Kobach's team or explain trial procedures, leading to an angry exchange Thursday between the judge and Kobach's team over their efforts to introduce new evidence that has not been shared with the plaintiffs' attorneys.

This continued on Friday, when Roe tried again through a different method to introduce updated numbers of noncitizens who registered or tried to register, prompting Robinson to lecture them that it was their duty to update or supplement those numbers before the trial began.

Earlier Friday, Robinson interrupted testimony from Bryan Caskey, elections director for Kobach, who would not answer directly when asked if Kobach's office had notified suspended voters that they could vote in elections. The judge issued the order in a preliminary injunction in 2016 that temporarily blocked the law's implementation.

Robinson took over questioning and Caskey eventually said he wasn't sure if the office had notified the suspended voters.