Updated

Republican Rep. Jason Chaffetz is pressing the Department of Homeland Security for an explanation following a disputed report that at the behest of  the department agents waited to arrest an illegal immigrant intern working for a prominent U.S. senator until after the election.

The department has "categorically" denied this allegation, made by an anonymous source in an Associated Press article earlier this week. The intern in question is Luis Abrahan Sanchez Zavaleta, 18, who worked for Democratic New Jersey Sen. Robert Menendez. Sanchez was arrested in front of his home in New Jersey on Dec. 6.

Officials were originally planning to arrest him on Oct. 25. It remains unclear what prompted the delay.

Chaffetz, R-Utah, chairman of a House oversight subcommittee on homeland defense, called the claims in the original AP story "disturbing" and in a letter to DHS Secretary Janet Napolitano asked for a written explanation by Jan. 3.

Chaffetz asked whether anyone at the department ordered Immigration and Customs Enforcement not to apprehend the suspect. Further, he asked who at DHS made that alleged decision and why, and whether the Nov. 6 elections played any role.

ICE spokesman Brian Hale, however, called the claim "categorically false."

"ICE followed standard process in coordination with its federal partners and local prosecutors before taking appropriate enforcement action," he said in a statement.

It's unclear whether the arrest would have made a difference. Menendez won re-election with a comfortable 58 percent of the vote.

Menendez' office has meanwhile distanced itself from the intern.

Spokeswoman Tricia Enright said that he was an unpaid college intern in their Newark office for two months.

"No staff member responsible for managing the internship program had reason to believe, based on their interview process, that Sanchez had any criminal background or immigration issues.  Clearly Mr. Sanchez sought to deceive our staff," she said in a statement.

Enright said Sanchez' "relationship with our office immediately ended" as soon as the senator's office was informed of his arrest. She said Menendez is "appalled" by the incident.

"He has no tolerance for those who violate the law and expects the authorities to continue to prosecute the case. Senator Menendez believes this incident underscores the reason we need comprehensive immigration reform that provides zero tolerance for those who have criminal records," she said.

The prosecutor's office in Hudson County, N.J., said Sanchez was found to have violated the law in 2010 and subsequently required to register as a sex offender. The exact charge was unclear because Sanchez was prosecuted as a juvenile and those court records are not publicly accessible. The prosecutor's office confirmed to AP that Sanchez registered as a sex offender, although his name does not appear on the public registry. The acting county prosecutor, Gaetano Gregory, is a Republican.

Authorities in Hudson County notified ICE agents in early October that they suspected Sanchez was an illegal immigrant who was a registered sex offender and who may be eligible to be deported. ICE agents in New Jersey notified superiors at the Homeland Security Department because they considered it a potentially high profile arrest, and DHS instructed them not to arrest Sanchez until after the November election, one U.S. official told the AP. ICE officials complained that the delay was inappropriate, but DHS directed them several times not to act, the official said.

During discussions about when and where to arrest Sanchez, the U.S. reviewed Sanchez's application for permission to stay in the country as part of President Obama's policy to allow up to 1.7 million young illegal immigrants avoid deportation and get permission to work for up to two years. As a sex offender, he would not have been eligible. Citizenship and Immigration Services, which oversees the program known as Deferred Action for Childhood Arrivals, notified Sanchez of that shortly before his arrest, one official said.