Oslo was the artist on residence and the admin for a gala at the same college Alexis Taymor went to. He's one of few people who knew she had an alternate personality, Monica Dow, who came out more when she went to college and under whom she went to college as. Oslo was dazzled by Dow's work and felt Taymor's illness to be a gift he didn't want stifled. But Taymor's best friend, Corinne Palmer, was helping her treat her condition in hopes Taymor would be herself more than her alter, and she'd eventually be cured enough to succeed and live her life.
When the drugs stopped working, Palmer continued to support Taymor and took a more active role in being a companion in her therapy. Decided Palmer had to go, Oslo gave her a laptop with the keys poisoned with thallium, but he decided to up the ante once that also was too slow. As one final attempt for Dow to lock in Taymor's conscious and unravel her into her illness, he stalked the two women when they were relaxing at the pool. Taymor heard him rustling in the bushes and got out to find her phone and call security.
He then jumped out and dunked Palmer into the water to drown her, then stabbed her to death with a paint knife he stole from Hatch.
This finally did make Taymor snap and dissociate back into Dow more permanent than she ever had. When he was interviewed by Frank Tripp , he was insistent on getting Taymor now as Dow back into the gala for her big exhibit that was coming up, but Tripp said she was scheduled for a polygraph test as a condition. Eventually, when the CSIs discovered and brought out Taymor herself and thus closed in on him, he dropped the paint knife he used as a weapon in Hatch's art supplies to frame him for the murder and other crimes.
Hatch confessed about Oslo's bribery and the pill tampering, but denies killing Palmer, which they believe, as they now suspect Oslo is the mastermind behind all the crimes. They not only confront Oslo, they test his jacket and find traces of chlorine in his cuff, which he got from drowning Palmer by her hair. He starts ranting about all the famous artists with mental instability and says Dow could've been one of the greats if Palmer wasn't helping Taymor get treatment.
