Pardon

A pardon is a government decision to allow a person to be relieved of some or all of the legal consequences resulting from a criminal conviction.

Notable examples
After Space Major Jon Bowman stopped Dalek X's plot at the end of the Second Dalek War with the help of the Tenth Doctor, he was given a full pardon by Earth Command for his actions and chose to retire on Earth. (PROSE: Prisoner of the Daleks)

In exchange for help in dealing with the Weeping Angel onboard the Byzantium, River Song was offered a pardon for the crime that had put her into the Stormcage Containment Facility, stated to be the murder of the best man she knew. At the end of the adventure, River suggested to the Eleventh Doctor that although she was being returned to custody, she may have done enough to earn her pardon. (TV: The Time of Angels/Flesh and Stone)

When the Doctor encountered River again in 1938 Manhattan, she told him that she was pardoned "ages ago" because the Doctor had erased every single trace of his existence from every database in the universe. As a result, there was no proof that the man River had killed ever existed. (TV: The Angels Take Manhattan)