Quirrell attempts to assassinate Harry during the Quidditch match in Philospher's Stone.
"But Snape tried to kill me!"
"No, no, no. I tried to kill you. Your friend Miss Granger accidentally knocked me over as she rushed to set fire to Snape at that Quidditch match. She broke my eye contact with you. Another few seconds and I'd have got you off that broom. I'd have managed it before then if Snape hadn't been muttering a counter-curse, trying to save you."
"Snape was trying to save me?"
"Of course," said Quirrell coolly. "Why do you think he wanted to referee your next match? He was trying to make sure I didn't do it again. Funny, really...he needn't have bothered. I couldn't do anything with Dumbledore watching. All the other teachers thought Snape was trying to stop Gryffindor winning, he did make himself unpopular...and what a waste of time, when after all that, I'm going to kill you tonight."
Quirrell snapped his fingers. Ropes sprang out of thin air and wrapped themselves tightly around Harry.
"You're too nosy to live, Potter. Scurrying around the school at Hallowe'en like that, for all I knew you'd seen me coming to look at what was guarding the Stone."
(Philosopher's Stone, Chapter 17, The Man with Two Faces).
Quirrell's stated chain of logic is that:
- Harry had been scurrying around the school at Halloween.
- This made Quirrell think that Harry may have realised that Quirrell wanted the Stone.
- Quirrell concluded that Harry was "too nosy to live".
- Quirrell tried to kill Harry during the Quidditch match.
Yet why was Harry singled out for murdering? If Harry was too nosy to live then surely Ron and Hermione were too? The event which sparked off Quirrell's attempted assassination was Harry being out his dormitory during the Halloween troll attack. Yet Ron and Hermione were also out and about that evening. (Hermione was only there because she wasn't aware of the edict to go back to the dormitories - but Quirrell wouldn't have known this since Hermione lied to McGonagall about her reasons for being there). Surely if Harry being caught fighting the troll made him a target then Ron and Hermione should have been targets too?
Yet Quirrell chose to try and kill Harry on the Quidditch pitch, the one place where he knew the trio couldn't be attacked together. His methods and his language suggest that he wasn't interested in Ron or Hermione.
He wasn't acting out of ignorance. Quirrell knew that Ron and Hermione were with Harry on Halloween because he discovered the trio together with the troll that night, alongside the other teachers.
A moment later, Professor McGonagall had come bursting into the room, closely followed by Snape, with Quirrell bringing up the rear. Quirrell took one look at the troll, let out a faint whimper and sat quickly down on a toilet, clutching his heart.
(Philosopher's Stone, Chapter 10, Hallowe'en).
Since Quirrell knew that Harry, Ron and Hermione had been out-of-bounds together at Halloween why didn't he try and kill all three of them? Why did he only try to kill Harry?