Why Pettigrew never tried to kill Harry

'Professor Lupin?' said Hermione timidly. 'Can - can I say something?'
'Certainly, Hermione,' said Lupin courteously.
'Well - Scabbers - I mean, this - this man - he's been sleeping in Harry's dormitory for three years. If he's working for You'Know-Who, how come he never tried to hurt Harry before now?'
There!' said Pettigrew shrilly, pointing at Hermione with his maimed hand. 'Thank you! You see, Remus? I have never hurt a hair of Harry's head! Why should I?'
'I'll tell you why. Because you never did anything for anyone unless you could see what was in it for you. Voldemort's been in hiding for twelve years, they sat he's half-dead. You weren't about to commit murder right under Albus Dumbledore's nose, for a wreck of a wizard who'd lost all his power, were you? you'd want to be quite sure he was the biggest bully in the playground before you went back to him, wouldn't you? Keeping an ear out for news, weren't you, Peter? Just in case your old protector regained strength, and it was safe to rejoin him...'

THE SERVANT OF LORD VOLDEMORT - Pg 392