You're going to need to find Isaias Sandoval, an associate and aid of William Taggart. He is apparently hiding in the sewers.
o Meet Sarif in the Penthouse [250XP]
o Meet Malik at the Helipad [250XP]
You could now hack all PC's in Sarif Industries for additional experience and background information. Also read your own email and talk to Athene nearby the helipad for an additional conversation. Head back to Malik to continue [250XP].