A Delta passenger who fought with a flight attendant and attempted to open an emergency exit midair will spend 18 months in federal prison.

Mario Nikprelaj, 24, of Shelby Township, Michigan, received the sentence Tuesday after pleading guilty to interfering with flight crew and attendants on a SkyWest flight operating as a Delta Connection from Omaha to Detroit on July 17, the U.S. Attorney’s Office for the Northern District of Iowa announced.

Prosecutors said Nikprelaj’s disruptive behavior began even before takeoff, when he refused to keep his seatbelt fastened and made rude remarks to crew members. Once the plane was airborne, he repeatedly stood up, ignored crew instructions, and poked a flight attendant in the chest while threatening to kill them.

Nikprelaj seemed to fall asleep in his seat, but the situation quickly escalated when he began tampering with the emergency exit door, causing several passengers to press their call buttons.

An 80-year-old flight attendant, whom he had previously threatened, approached him to intervene, but he pushed them aside, cursed at them and continued making threats.

Fearing a safety breach, the captain diverted the flight to Eastern Iowa Airport in Cedar Rapids for an emergency landing. During the descent and after landing, Nikprelaj remained belligerent, removing his shirt, walking up and down the aisle, and confronting three passengers who attempted to help restrain him, prosecutors said.

Cedar Rapids police took Nikprelaj into custody after the plane landed. Authorities also discovered a prescription bottle containing 41 pills of purported Xanax that was not prescribed to him.

Nikprelaj will also serve two years of supervised release following his prison term, as federal inmates are not eligible for parole.

In addition to his federal conviction, he has a history of legal troubles, including charges for assaulting a police officer, domestic violence, and drug-related offenses, according to court records cited by prosecutors.