You can delete records from the recycle bin by using the Database.emptyRecycleBin method:
Database.emptyRecycleBin([
SELECT Id FROM Candidate__c WHERE Id = 'a012800000Gs7IG' ALL ROWS
]);
If your record is still in the recycle bin after calling the above, you should open a ticket with support. You can also hard delete via the Bulk API if you enable it as an option.