KANSAS CITY, Kan. (AP) — An expert on voter fraud says voter confusion and clerical errors likely led to a “handful” of noncitizens successfully registering to vote Kansas.

Lorraine Minnite, a professor of political science at Rutgers University, testified Friday in the trial for a lawsuit brought by the American Civil Liberties Union challenging a law requiring people to provide documents verifying citizenship when registering.

Minnite believes voter fraud is rare in the United States. She said her research on the subject didn’t support Kansas Secretary of State Kris Kobach’s public assertions that noncitizens registering to vote is a pervasive problem in the country.

Earlier Friday, Brian Caskey, director of elections in Kobach’s office, testified that he wasn’t sure if the office had notified all suspended voters that they could vote in elections.