Democratic Sen. Robert Menendez of New Jersey said Wednesday he had no way of knowing that an unpaid intern had overstayed his visa and was a sex offender.

According to the Associated Press, U.S. Immigration and Customs Enforcement (ICE) agents arrested the 18-year-old intern, Luis Abrahan Sanchez Zavaleta, last week. The teen from Peru was required to register as a sex offender in 2010, but the charges are not in the public record because Sanchez was a juvenile at the time.

"Here's what we know," Menendez said on MSNBC. "We know we have a non-paying college intern program. This young man applied to that process and got recommended by the school. We asked [the immigration] status of all of those college interns and nothing indicated anything about his status, and we certainly wouldn't have known through any background checks, since he is a minor, about any sex offender status. Once it came to our attention, our New Jersey staff director let the young man go from the program. That's all we know."

Menendez has been a vocal advocate of immigration reform and said the incident spoke "volumes of how much we need" to address the issue.

"I can't know who is here to pursue the American dream versus who is here to do it damage if I cannot get people to come forth out of the shadows, go through criminal background checks and then determine who is here to pursue the dream and make sure that those who are here and have criminal backgrounds ultimately get deported," he said.

Along with other Senate Democrats, Menendez introduced legislation last year that would require undocumented immigrants in the U.S. to register with the government. The bill would provide most undocumented immigrants with a path to citizenship, but deport those who had a criminal background. Critics have derided the proposal as "amnesty."

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