Dr. Cohen's team was working on a biotoxin called Thoros-B, based on "an exotic lifeform discovered on the frontier". Since Binary Helix saw no profit in a toxin that only killed one species, Cohen's team developed it to affect more species. While they were working on the biotoxin, Mira's core went offline, and quarantine was broken. The Thoros-B infected several of the scientists, but was not contagious. Dr. Cohen had to take over after the station's doctor was killed; he had little medical training, but did his best to take care of the others. He was also tasked with administering stims to the guards on request. Cohen had little choice as the perimeter needed to be maintained, but he became worried about how stressed Captain Ventralis and his soldiers had become: the guards had been awake for days.
When Commander Shepard's squad arrives, Cohen asks for help in making the biotoxin cure, because he cannot access the quarantined lab. In return, he can offer his pass to the secured maintenance area at the back of the station, warning that Ventralis' men are getting more on edge since Shepard arrived.
If Shepard makes the cure, the squad is ambushed by Alestia Iallis, but Dr. Cohen is as shocked as they are that she turned out to be an asari commando. He explains that Alestia was recently transferred to Peak 15 by Saren Arterius. If Shepard accuses him of setting them up, or avoids mentioning the asari, Dr. Cohen maintains that he abhors conflict to the extent that he never even fired people before - personally, as he lets his receptionist do it.
In any case, Dr. Cohen thinks the guards might have been expecting Shepard, as they have been more on edge since the team arrived. He is very grateful for the Commander's help and offers a reward — Shepard can charm or intimidate him to get some extra medi-gel packs. As he is a project lead, Dr. Cohen also has a pass to the sealed maintenance area connecting the quarantine lab to the secure lab, which Shepard can borrow for access.
If fighting breaks out between Shepard and Rift Station's guards, Dr. Cohen along with most other civilians in the area will refuse to have further dealings with the squad. He will refuse to accept the cure even if it has been completed.