WASHINGTON - Washington is deeply concerned over the release this week of a Sudanese man facing the death penalty in connection with the killing of a U.S. diplomat in 2008, the State Department said on Wednesday.

Abdelraouf Abuzeid was found guilty, along with others, in the killing of American John Granville and a Sudanese colleague, who both worked for the U.S. Agency for International Development and were killed by gunmen in Khartoum.

"I was horrified," Granville's mother, Jane Granville, told Reuters about hearing of Abuzeid's release.

Abuzeid's brother told Reuters on Monday that his sibling was released by the country's high court based on a multi-million dollar 2020 settlement between Sudan and victims of attacks including the one that killed Granville.

The assertion that the United States had agreed to his release as part of the settlement was inaccurate, State Department spokesperson Ned Price said in a statement.

The money received by Granville's family from the Sudanese government was interpreted by a majority of the court as a release of their right to retribution and the acceptance of blood money, said a Sudanese legal source related to the case.

"In no way did (the settlement) say that that money was going to release any of these men that killed John," Jane Granville said. "I never would've accepted it if that was part of it."

Abuzeid's brother said he did not know whether Granville's family had agreed or not.

Price said the U.S. government is deeply troubled by a lack of transparency in the legal process that resulted in his release.

"We will continue to seek clarity about this decision," Price said.

Since an October 2021 coup, Islamists have regained power in government institutions including the judiciary. Abuzeid's father is a prominent Islamist leader.

Abuzeid remains listed as a Specially Designated Global Terrorist by the United States, and a reward was being offered for two others convicted of the killing that had previously escaped, Price said.

(Reporting by Daphne Psaledakis, Kanishka Singh, Nafisa Eltahir, and Khalid Abdelaziz; Editing by Chizu Nomiyama and Daniel Wallis)