Travis King, the American soldier who fled to North Korea, had been detained for getting into fights in South Korea before he crossed the border.
Court documents showed he also damaged a police car and had recently spent time in a detention facility in Seoul.
The 23-year-old serviceman had been recently released and was being sent back to the US when he escaped.
He joined a tour of the Joint Security Area and fled into North Korea, which has not commented so far.
It remains unclear what his intentions were for crossing the border. US authorities have said that he did so “wilfully, of his own volition” and expressed concern about his well-being.
Private 2nd Class (PV2) King’s mother Claudine Gates told ABC News she could not imagine her son doing such a thing. He “had to be out of his mind”, she said.
Ms Gates said she had last heard from the US soldier “a few days ago”, when he told her he would soon be returning to Fort Bliss, his army base in Texas.
PV2 King was reportedly investigated for assault in South Korea in September 2022. According to local media, he was suspected of punching a Korean national in a nightclub in Seoul.
He was fined 5m won (£,3,000; $3,950) for “repeatedly kicking” the back door of a police car and screamed “foul language” at the officers trying to apprehend him.
Local reports quoting officials said he was released on 10 July after serving two months in jail on assault charges, but did not elaborate.
After his release, he was placed under military observation for about a week in South Korea.
He was escorted to the airport in Incheon, near Seoul, for a flight back to the United States, where he was to face disciplinary action.
But he did not board the plane. The Korea Times, quoting an airport official, said he arrived at the boarding gate alone as military police officers were not allowed to accompany him all the way to the plane.
At the gate, he reportedly approached an American Airlines official and claimed his passport had gone missing. An airline employee then escorted him out of the departures area.
After parting ways with his escort, he is reported to have left the terminal to embark on a tour of the Demilitarised Zone, or DMZ, between North and South Korea, where foreigners can visit via tour companies.
It is not clear how PV2 King managed to get on one of these tours, as it typically takes between three days and a week for an individual to be authorised, and the trips are usually closely monitored.
An eyewitness on the same border tour described hearing the soldier laughing loudly before making a run across the border.
The United Nations Command, which operates the DMZ, said it believed the soldier was now in custody of the North. A senior US commander said there had been no contact with the soldier and the incident was being investigated by US Forces Korea.
Retired General Robert Abrams, a former commander of United States Forces Korea, told BBC Radio 4’s The World Tonight he believed we were “seeing the opening act” of a “tragedy of the utmost proportion”.
“I’ve got serious concerns for [PV2 King’s] health and welfare… I was actually glad they didn’t shoot him on sight when he came sprinting across the military demarcation line,” Ret. Gen Adams said. “He’s in for a very rude awakening on how North Koreans treat people who unlawfully enter the country.”
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