Khartoum — A man convicted as an accomplice in the escape of four men who were sentenced to death over the killing of a U.S. diplomat and his driver five years ago, has been pardoned by Sudanese president Omer Hassan al-Bashir, a lawyer told a local newspaper.

In statements carried by pro-government Akhir-Lahza newspaper on Friday, Abu Bakr Abdel-Razik said that his client Mubarak Mustafa was released last week after the presidential pardon.

Abdel-Razik did not provide further details or explain why Mustafa was a beneficiary of this amnesty. He was one of four men sentenced in this case.

John Granville ,of the U.S. Agency for International Development (USAID), and his driver, Abdurrahman Abbas Rahma on 2008 New Years Eve came under a hail of bullet before dawn on 2008 New Year's Day in a rare crime of its kind in Sudan directed at foreigners.

Sudanese authorities eventually managed to capture five men, believed to be belonging to the Islamic militant group Ansar al-Tawhid, and charged them with the killing of Granville and his driver.

Four of them were sentenced to death by hanging in 2009 but a year later they managed to escape the death row from the maximum-security Kober prison in the Sudanese capital.

The Sudanese government at the time said the prisoners used sewer pipes to escape.

One of the fugitives was reportedly killed in Somalia under mysterious circumstances while another was re-arrested.

The United States had called on the Sudanese government to "initiate a thorough investigation of the circumstances surrounding this escape" and "to prosecute, to the full extent of the law, any individuals or groups found complicit in the escape of these criminals".

A former U.S. official told Sudan Tribune last month that Washington believed that the inmates received inside to flee the prison but had no evidence linking anyone in the Sudanese government.