While the case has 3x 5.25" internal bays, there are only 2x 5.25" external bays that can be used. The top one can't be used due to the 2 reasons:
1. Front I/O wiring gets into the way of the topmost 5.25" bay.
2. You can't remove the front grille covering the topmost 5.25" bay, unless you cut it out of the front panel.
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And the bottom 5.25" bay has been converted to 3.5" bay with the metal clips at the bottom of the drive bay. If you'd remove those 2x metal side holders of 3.5" bay then you can put 5.25" drive there but you can't fasten it since the bottom bay doesn't have any screw holes on the sides.
Here's also a great review of Tesseract SW case with more...