Check the clock on the left side of the Bexhill murder victims room. Select the clock face itself, and set the time to 12:00. That counts as the first.
While investigating the third murder you'll search a mansion. After searching the inside throughly, Poiroit heads outside. Head to the right until you spot the planter box that isn't aligned properly with the path. (Poiroit will say something about feeling uneasy) Simply select the planter and straighten it out for the achievement.