The Dallas County district attorney’s office use of preserved DNA evidence to help free innocent people will be the subject of a TV documentary.

Dallas County commissioners have approved a request from District Attorney Craig Watkins to allow filming, in his offices, for the Discovery Channel program.

The contract, approved Tuesday, will be with a company based in England — Touch Productions Ltd.

Watkins established the conviction integrity unit so prosecutors, aided by law students, can examine hundreds of old cases where convicted criminals have requested DNA testing.

Details were not immediately available on when the planned two-hour program will air.