"I was a man once and I am aeast now"

“I was a man once and I am aeast now”. What circumstances turned the man into a ‘beast’ in ‘The Bishop’s Candlesticks’?

The circumstances which turned the convict into a ‘beast’ were the unjustifiable prison sentence of ten years awarded to him for a minor theft and the inhuman treatment he suffered in prison, where he was served bad and stale food and beaten mercilessly when he complained about it.