paragraph: The film opens with Sunita , a medical student , and her friends working on a project about the human brain .  She wants to investigate the curious case of Sanjay Singhania , a notable city businessman , who is reported to have anterograde amnesia .  Her professor denies access to Sanjay's records as it is currently under criminal investigation .  Sunita , nonetheless , decides to investigate the matter herself .  Sanjay is introduced as he brutally murders a man .  He takes a Polaroid picture of the man , and writes on it `` done '' .  It is revealed that Sanjay has anterograde amnesia where he loses his memory every 15 minutes .  Sanjay uses a system of photographs , notes , and tattoos on his body to recover his memory after each cycle .  It is revealed that Sanjay is ultimately out to avenge the death of his sweetheart Kalpana , and that he is systematically killing the people who were responsible for it .  His main target is `` Ghajini '' , a notable social personality in the city .  Police Inspector Arjun Yadav , on the case of the serial murders , tracks Sanjay down to his flat and attacks and disables him .  Yadav finds two diaries where Sanjay has chronicled the events of 2005 and 2006 .  The film flashes back to 2005 as Yadav reads the diary .  Sanjay Singhania is shown as the owner of the Air Voice mobile telephone company .  In the course of his business , Sanjay sends his men to meet Kalpana , a struggling model , about putting up a billboard above her apartment .  The owner of Kalpana's advertising firm misinterprets this as a romantic advance , and in view of a possible lucrative Air Voice ad campaign and other benefits , encourages Kalpana to accept the overture . 
question: Which person investigates the case of Sanjay Singhania?
answer: The professor