New details have emerged about a US soldier who crossed into North Korea on Tuesday -- but his exact whereabouts remain a mystery since the secretive country hasn't said a word about the incident.

Court documents showed that Private Travis King, believed to be the first US soldier to cross into North Korea since 1982, had a history of assault, was facing disciplinary action over his conduct and was meant to go back to the US the day before the incident. An army official told CNN the private was set to be administratively separated from the US Army.

Details about how exactly King ended up on the North Korean side of the border remain unclear.

King had been on a tour of a border area as a civilian when he crossed the demarcation line.

His motive is also a mystery. King's mother, Claudine Gates, told ABC she was "shocked" after being told by the US Army that her son had crossed into North Korea.

"I can't see Travis doing anything like that," Gates told ABC, adding that she heard from her son several days ago and he told her that he'd be returning to his base in Fort Bliss.

The US has been actively reaching out to North Korea to resolve the situation, but it has not yet heard back, a defense official said Wednesday. It is typical of North Korea not to respond to US outreach, the defense official added.

Adm. John Aquilino, who is in charge of US Indo-Pacific Command, said Tuesday that the US has had "no contact at this point" with North Korea in regards to King. Speaking at the Aspen Security Forum on Tuesday, Aquilino said King "made a run across the demilitarized zone in the Joint Security Area, was picked up by the North Koreans, and we've had no contact at this point."

Aquilino added that he has "gotten no reports" that King was a North Korea sympathizer.

The US Army has identified King as a cavalry scout who joined the military in January 2021. US officials did not say how long King had been in South Korea, but at some point he faced disciplinary action for assault and spent about 50 days in a detention facility.

King was held in a designated detention facility under the Status of Forces Agreement with South Korea, the officials said, which is an agreement that defines how US service members, their family members, and other Defense Department personnel are treated and processed in a foreign country, including its justice system

A US official told CNN that King was released from detention on July 10 and was set to fly back to the US on Monday.

Another official told CNN King was escorted to the airport by military officials, but the escorts were unable to accompany him to the gate and he ultimately did not board his flight.

History of assault

King appears to have a history of violent behavior. South Korean court documents show that he was accused of assault twice last year, and received a fine for one of the incidents.

Last October, he was accused of pushing and repeatedly punching a victim in the face in a club in Mapo-gu, Seoul, after being refused a drink he asked for, according to the Seoul Western District Court documents.

Following the alleged assault, King was taken into police custody and placed in the back seat of a patrol car, when he allegedly used offensive language against Korea, the Korean army and the Korean police while in anger, the court document said.

He then allegedly kicked the door of the patrol car several times, causing 583,959 Korean won (around $461) of damage, according to the court document. King was fined 5 million Korean won (around $4,000) as a result, the document stated.

"If the defendant does not pay the above fine, the defendant shall be detained in a labor facility for a period of time converted to 100,000 Korean won per day," the document said. It is unclear at this point if King paid the fine or served time at a labor facility.

The court document also referenced an earlier assault case against King from September 2022, which was dropped after the alleged victim expressed his intention not to press charges against King. South Korean police told CNN that King was transferred to US military police after an investigation into an assault last September. It is unclear whether the incident they were referring to was the same case that was dismissed by the court.

It is unclear whether the time he spent in detention was related to these incidents.