The Empire's Locate and Detain List was one of the many "temporary" security measures implemented by Emperor Palpatine. It kept amateur COMPNOR operatives occupied with responding to citizens turning in their neighbors as suspected Rebels, rather than tripping up one of the Emperor's meticulously planned schemes.
After the death of the Emperor, the Locate and Detain List became something of a "checklist" for bounty hunters and assassins. A sufficiently skilled hunter could acquire a small fortune — or more — by capturing one of the Rebels on the list.
Gunner Groth carried a copy of the list, and made an attempt to capture one of the list's newest additions, Mara Jade. Unfortunately for Groth, he was not sufficiently skilled for the task, and did not survive the encounter.