When Ryan tries Anne's door, it's unlocked. He wonders why she would leave without locking up. But the last seen of Anne, she went to Anton's studio to perform for him. So she did leave without locking up: she just didn't leave town as Anton claims. Anton brought her body to her apartment, but then why would Anton leave the door unlocked?
Jack says that all of the dancers who have died are "the best". But Ryan just read him the list of disappearances, and didn't mention any of the dancers' names. Sao Jack wouldn't know if they're the best, worst, or anywhere in-between.
The cousins claim that Anton has made the dancers' deaths look like suicides. And they find Anne's body hanging in her closet at her apartment. However, Anton has a bad leg because of a dance injury, and walks with the aid of a cane. It seems impossible that he could carry a body to a victim's apartment, or string them up.