There are some missions in Prey that are a bit difficult to complete without knowing where to look for just the right keycard. The optional The Corpse Vanishes mission is one of them. This will take you to the Psychotronics area of Talos I, where you must access the Morgue, but the keycard is nowhere to be found. There is a solution, however (obviously).
Opening the Morgue (or Letting the Bot Do Your Dirty Work)
There are three ways to get into the Morgue to compete the side quest, actually. The first requires you to read an email from Annalise Gallegos labeled "RE: I'm an idiot" on a workstation in the area. The email says that a Science Operator robot comes by every half hour. So if you follow it, you won't need a keycard since it will open the Morgue for you. The bad news is that this takes some time, and you may not want to wait around, especially since the robot is random in its patrol patterns and may not access the Morgue when you need it to. So there are two other options.
The second way is to use on of your Neuromod Typhon Mimic ability that lets you changes shape. Break the window with the bars, change into a mug or something small, then head through the bars.
Perhaps the best option, however is to use your Huntress Boltcaster weapon to launch a FlexiFoam bolt at the button after smashing the glass. The button unlocks the door, and voila, you have Morgue access and can loot the Neuromods and grab the Morgue keycard. You will also be able to loot Sylvain Bellamy's cabin keycard off another body, thus solving the mission.