An American citizen detained in North Korea this past April was sentenced to six years in prison with labor by that country's Supreme Court Sunday. 

Matthew Miller, 24, of Bakersfield, Calif., was found guilty of entering North Korea illegally and trying to commit an act of espionage. The court said that Miller tore up his tourist visa at Pyongyang's airport when he entered the country on April 10 and intended to ""experience prison life so that he could investigate the human rights situation." 

The trial lasted approximately 90 minutes. Miller, who waived the right to a lawyer, was handcuffed and led from the courtroom after his sentencing. The court ruled that it would not hear any appeals to its decision.

Earlier, it had been believed that Miller had sought asylum when he entered North Korea. During the trial, however, the prosecution argued that it was a ruse and that Miller also falsely claimed to have secret information about the U.S. military in South Korea on his iPad and iPod.

In an interview with the Associated Press published August 1, Miller said that he expected to be sent to prison, adding "I have been requesting help from the American government, but have received no reply." It was not immediately clear whether his comments were his own or had been coerced by his captors. 

Carol Stewart, a neighbor of Miller's in Bakersfield, told the Associated Press in July that Miller first traveled to South Korea about four years ago to visit a brother stationed there with the U.S. Air Force. He found work teaching English and learned Korean. She has since declined to comment out of respect for his parents' wishes.

A trial is also expected soon for Jeffrey Fowle, 56, who entered the North as a tourist but was arrested in May for leaving a Bible at a provincial club. A third American, Korean-American missionary Kenneth Bae, is serving out a 15-year sentence for alleged "hostile acts."

Fowle, a 56-year-old equipment operator for the city of Moraine, Ohio, said his wife, a hairstylist from Russia, made a written appeal on his behalf to Russian President Vladimir Putin. He said the Russian government responded that it was watching the situation.

The U.S. has repeatedly offered to send its envoy for North Korean human rights issues, Robert King, to Pyongyang to seek a pardon for Bae and other U.S. detainees, but without success.

Former President Bill Clinton came in 2009 to free a couple of jailed journalists. Jimmy Carter made the trip in 2010 to secure the release of Aijalon Gomes, who had been sentenced to eight years of hard labor for illegally crossing into the country to do missionary work.

In 2011, the State Department's envoy for North Korean human rights managed to successfully intervene in the case of Korean-American businessman Eddie Yong Su Jun.

The Associated Press contributed to this report.