Freedom Fighter Achievement

Freedom fighter is a very buggy achivement i tried using my 100% save file and do sequence 13 memory 2 book theif mission and reloading last checkpoint after killing the first leader during its introduction during save Leon section. I tried doing the coop dead kings dlc twice therefore killing 16 leaders and i tried a combination of both. Found out that only on non completed sequence 13 memory 2 can you use reloading last checkpoint to get the freedom fighter achivement. Second image shows u how to quickly kill the leader and reload last checkpoint, just walk to the right after reloading checkpoint the first time and preaim ur pistol and headshot him when he appears, u should be able to kill him before the pop up occurs that explains what leader enemies are. repeat until u get the achievement. Use ac savetool to use my save file.