You all need to consult with a coroner before making such statements.
You are right. That would be one of the persons that could answer such a statement. I think the idea first comes from many peoples experience over the past hundred years during HANGINGS. I personally was never there at one, so I can't say for sure. Do you know for sure ?
"It is also important to note that though the victim's anus was dilated, this by itself does not indicate or suggest anal penetration. The anus is a sphincter; a muscle which is tight and closed in most living individuals, and always open and dilated in deceased individuals.
When someone dies their anus relaxes and dilates. The presence of a dilated anus taken to indicate sexual assault or rape is a very common misinterpretation made by untrained individuals when examining those who have met with violent death."
Taken from: EQUIVOCAL EXAMINATION AND PSYCHOLOGICAL PROFILE OF CASE EVIDENCE Brent E. Turvey, MS Forensic Scientist & Criminal Profiler Knowledge Solutions