You can only do this mission if you saved Dr. Iwbe. After
Dahl arrives you will get a side mission which will have Iwbe requesting you to meet in your office where he will ask you to
incapacitate Dahl rather then kill him. This will all start to take place after you finish up on
Dahl's ship in the shuttle bay to which you have
15 minutes to reach life support to save the survivors in the Cargo Bay.
Thankfully Dahl is right there so head on down and
knock him out with your stun gun! Iwbe will tell you to leave the body there and after a little while he will call you to meet him in the
Neuromod Division and the area you are going requires you to unlock it with
HACKING II from the
security station. Meet with Iwbe and follow his instructions and that's it.