A Kansas man pleaded guilty Thursday to strangling his girlfriend then pushing her to her death off the balcony of a cruise ship that was off the coast of Florida last year, according to federal prosecutors.

Topeka resident Eric Duane Newman, 55, pleaded guilty to second-degree murder in the January 2018 killing of his longtime girlfriend, Tamara Tucker, 50, “with malice aforethought,” the Department of Justice said in a news release.

The couple was on a Carnival cruise from Jacksonville, Fla., to the Bahamas and staying in a cabin on the 13th deck.

Newman admitted during his plea hearing in federal court in Kansas that the couple had been arguing before the murder. He said he strangled Tucker then pushed her over the cabin room balcony railing to the 11th deck. Tucker died from blunt force trauma caused by the fall.

At the time, the cruise ship was about 30 nautical miles from New Smyrna Beach, Fla.

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Tucker was a full-time faculty member in the social work department at Park University in Parkville, Mo., from 2012 to 2017. Before that, she’d been an adjunct instructor since 2007.

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Newman’s sentencing is scheduled for March 18, 2020, before Chief U.S. District Judge Julie A. Robinson.

The Associated Press contributed to this report.