The achievement is for catching and arresting cliff harrison in the case file "a slip of the tounge" before police back-up arrives to stop him. Now from the start when the case begins chase him until you get up a slope he turns onto early and then from there just ram into his tail-end and try to knock him into a wall. This usually taks about 3 tries of ramming into his car but its quite easy. The majority of the time after the first straightaway he'll always turned left and thats when i would t-bone his car into a houses wall and once thats done just get out and run up to his car and POP achievement unlocked! Good luck and happy achievement hunting!