The U.S. military in Korea is examining the possibility that Private 2nd Class Travis King had planned for some time to defect to North Korea.

That may come as unwelcome news to Kim Jong Un's regime.

Thae Yong-ho, a former North Korean diplomat who defected some years ago to South Korea, wrote on Facebook:

"U.S. soldiers who have crossed/defected to North Korea are inevitably a nuisance because the cost-effectiveness is low in the long run."

Thae, who is now a lawmaker, recalled the case of another defector whose care and management proved an expensive burden for Pyongyang.

"A professional security and monitoring team had to be set up …  an interpreter, and a private vehicle, driver, and lodging had to be arranged," he wrote.

While King's decision to make a dash into North Korea may have some propaganda value for Kim Jong Un, the soldier also poses a problem for a regime bound by its own rigid rules.

To start with, his arrival broke North Korean law.

It is illegal to enter North Korea without documents or official approval. While this may sound absurd to most people, Pyongyang believes with some justification that it's necessary to deter people who might have a mission – think religious aid groups – from sneaking into the Hermit Kingdom.

One former U.S. official who specialized in North Korea told CBS News that when the U.S. complained about the treatment of several Americans who had entered the North illegally, Pyongyang responded by asking the U.S. to do a better job of keeping its citizens under control.

That means that King's fate won't be decided in a hurry. At the very least North Korea must go through the motions of trying him for illegal entry and sentencing him. Only then, perhaps, will it send him back across the border – technically known as the Military Demarcation Line – to face the music at home.

Professor Yang Moo-jin of the University of North Korean Studies in Seoul told CBS News that even if King defected with the intention of staying, he's likely to change his mind.

"He would not blend in with the North Korean society and would ask to be sent back to the States," he said.

Over the past three decades, 11 U.S. citizens were detained,  having accidentally or on purpose entered North Korea illegally. All of them were eventually released, though some required high-level diplomatic intervention.

Since then times have changed.   Diplomatic intervention has become virtually impossible since North Korea sealed its borders at the start of the pandemic. Almost all foreign officials were forced to leave the country. That includes representatives from Sweden, the "protecting power" for the United Sates in the North who could have lobbied for access to King.

Even though as a private, he has limited intelligence value to the North Koreans, King is bound to be de-briefed by state security.

They will evaluate whether he is really a defector, and whether his fantastic story about slipping out of the airport and onto a DMZ tour bus holds up. They will also have to satisfy the leadership that he is neither a provocateur nor an undercover agent.

Only then might he be allowed to stay. One expert suggested he could be useful as an English teacher, or perhaps as a copywriter for the English versions of state media. Back in the 1960s after the Korean War, some U.S. military defectors ended up playing the roles of Ugly Capitalist American Villains in North Korean movies.

If Pyongyang decides he's more trouble than he's worth, Professor Yang suggested Kim Jong Un might even use him to kick start negotiations.

North Korea could welcome a high-level U.S. envoy to negotiate King's return, Yang suggested, and use it as a catalyst for direct U.S.-DPRK talks.

But the U.S. says it's already open to talks. It's just that for the moment Kim Jong Un isn't interested. It's unlikely the unexpected arrival of a 23-year-old American defector will change his mind.

In:
• South Korea
• DMZ
• United States Military
• North Korea

Elizabeth Palmer has been a CBS News correspondent since August 2000. She has been based in London since late 2003, after having been based in Moscow (2000-03). Palmer reports primarily for the "CBS Evening News."