Maybe the "circumstantial evidence" that is left out in this text is the woman's emotional condition itself, who can say...
The most likely scenario I can see would be the accused having evidence of or on his person of a rape. Though the rape itself went unwitnessed by anyone other than the victim and perpetrator, had the perpetrator been seen, for instance, coming home in a state of emotional or physical dishevel, with wounds, or maybe with torn or even bloody clothing, and the coincidence of this was realized once the rape allegation was leveled, the person who made the observation might well have plied the person to ultimately, though reluctantly, admit what they did (either privately or publicly). Then there would be corroboration. But, then, the text seems more concerned with the woman's status (engaged or not engaged!!!) than the violence forced upon her!