That would be the Capital Punishment (Amendment) Act of 1868. It ended public executions, forcing them to be done within prison walls although whether reporters attended was left to individual prison governors. It wasn't until the 1910's that reporters were finally barred from witnessing hangings. The problems with public executions were many and varied. Drunkenness, theft, pickpocketing, violence and suchlike were standard practice among spectators and there was always a fear that the prisoner's friends and/or family might try and stop a hanging by freeing the prisoner. Doing the job within a prison improved security and allowed authorities total control over how the job was done, who attended and generally led to execution becoming an orderly, almost clinical affair. It evolved from a crude, disorderly public spectacle to a professionally-run affair done with clinical precision.