An American fugitive who has been missing and "wanted" since he deserted the US Air Force in 1984 has turned up in Sweden where he has been living under a under a new identity for nearly three decades.

"Sorry that I have been in hiding so long... I owe you all an explanation," David Hemler, now 49, married and the father of two daughters and a son, wrote to his American and Swedish families in a letter, which he later sent to AFP.

On May 11, Hemler showed up out of the blue at the law offices of Borgstroem and Bodstroem. He came forward because his secret "was too difficult to carry alone, and to not be able to have contact with his family in the United States for 28 years," said his lawyer Emma Persson.

"The time feels right," Hemler told AFP in an email.

Now, "we keep in touch regularly through telephone calls, email and Skype," he said of his US relatives. "Visits are planned."

But what happens next is unclear.

The airman remains listed as a "fugitive" by the Air Force Office of Special Investigations, whose web page shows a photo of the young Hemler as well as an "age progression photo" of the same man projected into his 40s.

US Air Force representatives have met here with his lawyer and requested a DNA test to confirm his identity, but Hemler's father in Pennsylvania and brother in New Jersey have told US media that there is no doubt the man who contacted them is indeed their long-lost son and sibling.

In Washington, the Air Force told AFP this week the matter is under investigation and "while the investigation continues, it is inappropriate for the Air Force to discuss the specifics of SrA Hemler's case," using his last rank of senior airman.

The US embassy in Stockhom has also refused comment, but lawyer Persson told AFP that "based on the little information ... obtained from the United States," her client "cannot be extradited according to Swedish law."

For Hemler, the rush of media attention since his story broke has taken up too much of his time, he told AFP, and refused further photographs.

His letter, however, gave a detailed account of why he went AWOL after enlisting in the Air Force during his last year of high school in Pennsylvania, at a time when he was unsure what to do with his life.

"It seemed like an easy way out of the labyrinth of choices that lay ahead of me," he wrote.

But a week after signing up for a six-year stint, he fell in love with a young pacifist who upended his conservative, traditional views.

"I discovered that there were alternatives to war," he wrote, and began looking at how he could end his military contract early but found there was no way out.