Tiny Taliqa Fields died in agony on Saturday just hours after her "spine-chilling" screams were overheard by neighbours.
Louis Burdett, 21, was pulled in for questioning by murder squad officers after the tot's life-support machine was turned off at Leicester Royal Infirmary.
She had been treated for horrific multiple injuries and bruises.
Taliqa lived in Leicester with Burdett, mum Zoe Harman, 23, and her two-year-old brother.
A neighbour told The Sun: “On Thursday evening, I heard Taliqa screaming and screaming. It was spine-chilling.
“I feel so awful now. I should have done something more. But there is so much animosity towards the police and social services around here that I didn't want to be targeted myself.”