Amir Mirzaei Hekmati's family has hired Pierre Prosper, a high-profile attorney and advisor to presidential candidate Mitt Romney's campaign, to seek the release of the American ex-Marine sentenced to death in Iran for espionage.

Hekmati has 20 days to appeal his case, brought on by Iranian authorities who claim he is a spy for the U.S. government, CNN reported.

We're prepared to open up a line of communication with the government, Prosper told CNN. Our hope is that they talk with us.

Prosper, who was hired to be one of 23 foreign policy advisors by Romney in October, successfully secured last year's release of Reza Taghavi, an Iranian-American businessman who was detained by Iran for more than two years. Prosper also informally advised the families of the three American hikers accused of spying on Iraq in 2009 and released last year, he told CNN in an exclusive interview. During the Bush administration, he served as an ambassador-at-large for war crimes.

The attorney said Hekmati's family reached out to him when they heard about his work with Taghavi. In a statement released last week, the family told reporters that they were working with a government-appointed lawyer after struggling to navigate complicated legal ropes.

We are deeply concerned that Amir is not receiving a fair trial and has not been afforded due process, Hekmati's family wrote. We have struggled to provide Amir with an attorney in Iran. We have sought to hire at least 10 different attorneys in Tehran to no avail.

Hekmati was arrested five months ago on a trip to Iran from Michigan. On December 18, Iranian state television aired a confession, in which Hekmati says he was commissioned by the government to gather information on Iran in the role of a double agent.

The ex-Marine's sentence come amid heightening tensions between the United States and Iran. Reports over the weekend revealed that Iran had built an underground uranium enrichment facility for their nuclear program, with the U.S. and allies worry is for developing weapons. Iran has threatened to shut down the Strait of Hormuz, a vital waterway in the oil trade, and has banned the U.S. from returning their aircraft carriers to the Persian Gulf, but the Pentagon has largely dismissed the warnings.

This case is entrapped in an intense political environment, Prosper told CNN.

The U.S. has denied that Hekmati, a 28-year-old who worked as an Arabic translator with the military, works for the C.I.A. The State Department called the spy allegations complete fabrication, The Associated Press reported Monday. His family said he was visitng relatives in Iran.