The San Antonio federal prosecutor at the center of a politically charged case against two Border Patrol agents convicted of covering up their role in the shooting of a drug smuggler resigned Thursday.

U.S. Attorney Johnny Sutton submitted his letter of resignation to President Barack Obama and U.S. Attorney General Eric Holder, said Shana Jones, a spokeswoman for the U.S. Attorney’s Office for the Western Judicial District of Texas.

Sutton’s resignation was voluntary, Jones said, and his future plans were not immediately disclosed. He was not available for comment.

U.S. Rep. Lamar Smith, R-San Antonio, the ranking Republican on the House Judiciary Committee, said Sutton “did a good job overall as U.S. attorney.â€