Anil Uskanli told a federal judge Tuesday that he was chasing and trying to kill a butterfly aboard an American Airlines flight from Los Angeles when the captain put the plane on lockdown and called for military fighter jet escort into Honolulu.

He told U.S. District Judge Derrick K. Watson that’s what he believed May 19 aboard American’s Flight 31. “Because I was ill, I was hallucinating,” he told Watson.

He said it’s not what he believes today.

Uskanli, 25, pleaded guilty Tuesday to interfering with the airline’s flight crew and flight attendants. The crime is punishable by up to 20 years in prison. Under the terms of his plea agreement, however, Uskanli will be allowed to ask Watson to sentence him to a jail term no longer than the time he has already been in custody.

Assistant U.S. Attorney Thomas Brady told Watson the government will not oppose the request and will not ask for additional jail time. He said the government might ask Uskanli to pay a fine and restitution.

Watson scheduled sentencing for Jan. 17 but said he will ask the court’s pretrial services to expedite Uskanli’s pre-sentence investigation and report to allow for an earlier sentencing. Uskanli’s criminal defense lawyer Richard Sing had asked for an earlier sentencing date so Uskanli can get back to his native Turkey as soon as possible.

Uskanli was in the United States on a student visa while attending acting school in California. U.S. immigration officials have revoked Uskanli’s visa and put a detainer on him to keep him in custody. Uskanli’s immigration lawyer, Gary Singh, said Uskanli will agree to leave the country as soon as he completes his criminal sentence.

Sing said Uskanli was diagnosed with a mental illness in 2015 in Turkey. He said Uskanli got a diagnosis for a different mental condition when a U.S. Bureau of Prisons forensic psychologist examined him on his competency to stand trial in the airline case.

Uskanli told Watson he was sitting in his seat when suddenly a butterfly came out of the pocket of the seat in front of him. He said the butterfly flew into the toilet where he followed it and tried to kill it. He said that could have been when another passenger opened the bathroom’s unlocked door and found him yelling and slamming on the bathroom’s walls.

Flight attendants told the FBI that other passengers had already asked to move away from where Uskanli was sitting because he was talking to himself. After the bathroom incident, they said, Uskanli went back to his seat and wrapped a blanket around his head.

Uskanli told Watson he used the blanket to cover his eyes because he wanted to sleep.

A flight attendant told the FBI that Uskanli later tried to go to the front of the cabin, so she put a service cart in the aisle to block his way. The attendant said she called for and got help from passengers when Uskanli pushed on the cart.

Uskanli told Watson he was following the butterfly to the front of the cabin and leaned on the service cart.

One of the passengers who helped prevent Uskanli from moving forward was an off-duty police officer. He escorted Uskanli to his seat and sat with him for the rest of the flight.

Before going back to his seat, Uskanli left his laptop computer on the service cart; the flight crew feared it might contain explosives. The crew barricaded the laptop, and the captain ordered the cabin to be placed on lockdown. He also took the plane to a lower altitude. His actions also prompted the scrambling of two Hawaii Air National Guard fighter jets from Joint Base Pearl Harbor-Hickam to escort the passenger airplane to Honolulu Airport.