The Thirteenth Floor

In late 1990's Los Angeles, Hannon Fuller (Armin Mueller-Stahl) is the owner of a multi-billion dollar computer enterprise and the inventor of a newly completed virtual reality simulation (VR) of 1937 Los Angeles. When Fuller is murdered just as he begins premature testing of the system, his friend and protégé Douglas Hall (Craig Bierko) finds himself the primary suspect, and begins to doubt his own innocence.Between questioning by LAPD Detective Larry McBain (Dennis Haysbert), Hall meets Jane Fuller (Gretchen Mol), who he is surprised to learn is Fuller's estranged daughter. Hall develops a romance with Jane, who we soon find out is attempting to shut down the new VR system. When a local bartender who witnessed a meeting between Hall and Fuller on the night of the murder is himself found murdered, Hall is imprisoned. He is soon released though, after Jane provides him with an alibi.Seeking answers, Hall attempts to track down a message left by Fuller inside the simulation. Within the system, Hall learns that Jerry Ashton, a bartender (Vincent D'Onofrio) has stumbled upon the truth about his artificial nature by reading the message intended for Hall. Frightened and angry, Ashton attempts to kill Hall, who barely escapes the system in time.Now unable to find Jane, Hall discovers her double, Natasha Molinaro (also Gretchen Mol), working as a grocery store clerk but Molinaro seems not to recognize Hall. This leads Hall to perform an experiment outside the VR system, something that Fuller had instructed him to try in his letter: He tried to drive to a place where he never would have considered going otherwise. When he arrived, he saw that the area and everything within it didn't exist, and was instead replaced by wire frame models.Finally understanding the meaning of Fuller's message, Hall realizes the truth that his own world of 1990's Los Angeles is itself a fabricated simulation.Several revelations follow: Hall's virtual world is one of thousands, but is also the only one that developed a virtual world of their own. Jane actually lives in the "real world", and only participated in the 1990s simulation in order to assume the identity of Fuller's daughter, gain control of the company, and shutdown the simulated 1937 reality. Hall himself is modeled after Jane's real-world husband David, who has begun to seek pleasure by murdering people in the 1990s simulation. It was David who had performed the murders, while controlling Hall's body, because he had become jealous when his wife Jane fell in love with Hall within the simulation.Whitney (also Vincent D'Onofrio), Hall's associate, enters the simulated 1937 and assumes the role of Ashton, who has kidnapped Ferguson and bound him in the trunk of his vehicle. When Whitney is killed in an automobile accident, Ashton's consciousness is released into Whitney's body (in the 1990's). Ashton kills a security guard, David (Bierko yet again) assumes control of Hall, kills Ashton, and attempts to rape and murder Jane. She is saved by Detective McBain, who shoots and kills David.The death causes Hall's consciousness to be released into David's body, and he wakes to find himself in 2024, connected to a VR system. He disconnects the system and finds Jane and her father, who looks very much like the man he was accused of killing in his original reality, Hannon Fuller.

Question: Who is the primary suspect in Hanon Fuller's murder?
Answer: Douglas Hall; Douglas Hall