It depended on your definition of culprit to decide if River Song was of interest. Generally speaking, she was mad, bad and dangerous to know and in this particular melee of PDAs she was clearly enjoying herself.

Both the spectacle and the occasional snog.

So anyone looking for suspicious people, might find her obvious enjoyment of the situation and not altogether hidden voyeuristic amusement a little suspicious.

You know, if the law wanted to investigate.