Use the following steps. Note: You must be friends with Eve.

During your training day, kill Buck with the fire extinguisher.
Listen to Eve's dialogue when you first meet her on the ground floor lobby of the apartments. You must also meet her in the relaxation room on day one.
Progress as usual until you get the safe key from Eve's room. Get both key cards to access to the lower levels.
Go through the lower levels.
After leaving the facility, keep moving to the left past the gate.
Once past the gate and into the woods, you will encounter the gangsters and the ending will start.