Take as many pictures of the Houdini Splicer as possible. Near the end of the game, when you are in Olympus there is an apartment that belongs to Cohen. There will be two Houdini Splicers dancing in the living room and they won't attack you so long as you keep a bit of a distance and don't attack them. So you can stand back and fill your research bar up there.
Also - if you did NOT kill Cohen earlier,when you attack the Houdini splicers, he will run out of a door and scream at you about it. Kill him, take his picture for the Irony achievement, then go up the stairs into his room for another achievement.