You should contact the Police. They are the specialist and have the power of law for that. Contacting HR for this may be seen as a personal Vendetta sd you sa

You should contact the Police. They are the specialist and have the power of law for that. Contacting HR for this may be seen as a personal Vendetta sd you say it happens outside the workplace. Contact police and give as much detail you can. I am sure police have more ways and skills to investigate that.