Much as we see on boards such as this and Social Media, people are very happy to believe unproven allegations especially of a sexual nature.
Five minutes into the opening of Ep 1 it was explained that the police were so sure they had the culprit that they did not go looking to disprove the circumstantial evidence of her whereabouts at the time of the murder (i.e. she being in the town centre, not the crime scene).
The photo placing her in town did not emerge until three years after the trial when her friend, the editor of a local newspaper, helped in her campaign to prove her innocence.