A man who told police he "felt good" after hurting his 10-month-old niece, murdered her while he was baby-sitting.
Stoker told police there was a "beast" inside him
Trevor Stoker, 38, killed Mollie Louise Norman when he covered her with a pillow and punched her repeatedly before hitting her head against a bed.
He claimed the "beast" inside him made him attack the child and told a police officer that hurting the child made him feel "good".
Stoker, from Salford, was found guilty by a jury at Manchester Crown Court.
He will be sentenced on Wednesday.
Mollie's parents, Carl and Rachel, had left their child to stay with Stoker and his wife, Shelley, at their home in Salford on 11 June 2005.
The next day, Stoker covered her body with a pillow then punched her several times through it.
Mollie Louise Norman was punched repeatedly through a pillow
The court heard, that he then picked her up by the ankles and struck her head onto the bed, causing severe internal brain injuries.
Mollie never recovered from the attack and died at Alder Hey Children's Hospital in Liverpool a few days later.
Stoker told a police officer in a phone conversation that inside him was a "beast that shows his ugly head every now and then".
He told the officer the beast told him to "give her a little squeeze and make her feel a little bit of pain".
"I'd do that a couple of times and I'd feel good, I don't know why, It's awful," he said.
Det Ch Insp Geoff Wessell, of Greater Manchester Police, said it had been an extremely traumatic investigation for everyone involved.
"Even the most experienced officers cannot help but be affected by what has happened and the family have obviously been left absolutely devastated by their loss," he said.