What could the North Koreans be thinking?

North Korea has detained 85-year-old American army veteran Merrill Newman. And no one is sure why.

Another US citizen, Korean-American Christian missionary Kenneth Bae, was seized last year and sentenced to 15 years in a labor camp.

The Obama administration's special envoy to North Korea, Glyn Davies, today suggested North Korea improve its relations with the US by releasing both men.

"North Korea could send a very different signal about its interest in having a different sort of relationship with the United States were it to take that step of releasing our citizens," Davies told Reuters. "And it's a matter of some wonderment to me that they haven't yet moved on that."

So why would North Korea bother detaining someone like Merrill Newman? Apparently, he'd already finished a 10-day visit, cleared customs and was then grabbed off the plane that was to take him out of the country.

Arresting an elderly Korean War vet with a heart condition hardly seems like the best way to encourage western tourists to visit the DPRK, which is the official name of North Korea.

Don Kirk, Asia correspondent with the Christian Science Monitor, speculated that Newman might have riled North Korean officials by arguing about the armistice that ended the Korean War.

"[The North Koreans] keep telling their people that the Korean War armistice was actually a surrender by the US and South Korea — and that North Korea scored a tremendous victory in the Korean War," Kirk said.

But Kirk doesn't find that theory especially likely — he figures if the North Koreans had been bothered by that, they likely would have told him as much sooner, and never let him on the plane.

Other than Newman and Bae, Americans have also been detained for illegally crossing the North Korean border or for bringing "propaganda" barred by the North Koreans, often religious materials. But given what's known about Newman and his circumstances, neither is believed to apply in his case. 

So that leaves the possibility that Newman may have taken some sort of souvenir that wasn't meant to be taken. On his trips, Kirk said he's been strongly warned not to do anything like that.

"They could have noticed stuff was missing and rushed onto the plane to get it," he said.

His other theory is that perhaps Newman wrote some sort of farewell insult that was noticed before his plane took off. Neither of Kirk's theories is based on any evidence, but rather on the sorts of things that might get a foreigner detained.

Newman hasn't been seen since he was pulled off the plane Oct. 26. And North Korea hasn't bothered to accuse him of anything publicly.