I had a friend who had the same problem as you.
You need to contact Comcast and put a complaint, including all the information you mentioned. Unfortunately, they are the only ones who know who specifically has the lease on that IP address. However, they might be cooperative if you mention that you are putting a complain with the police.
Go talk to the local police department and see if you can file a complaint of some sort.
Also, check your daughter's emails. All email addresses have "email headers." This means that every email address sent to her at any point in time has the IP address of the person who sent it. Chances are that she knows the person doing this, and she might have received an email from that person at some point in time.