"We have no idea that how with the guides and the visas and the paper and the itinerary that there could be anything that could've gone off track," Lee Newman told ABC News.
The Swedish Embassy was negotiating on a daily basis on behalf of Newman because the U.S. has no diplomatic ties to North Korea, the State Department said.
Jeffrey Newman said it was his father's dream to return to the country where he spent three years as an infantry officer during the Korean War.
"He'd been to the peninsula before about three years ago. He was in South Korea but he'd never been to North Korea and he'd always wanted to go back," he said. "He had a great respect for the Korean people and a keen interest in the Korean culture."
North Korea has detained at least six Americans since 2009, including two journalists accused of trespassing and several missionaries accused of spreading Christianity. Bae, a Korean-American missionary and tour operator, has been detained for more than a year.
The Associated Press contributed to this report from Seoul, South Korea.