Private Investigations and Personal Security/blackmail
I am a writer and I'm trying to research how realistic a situation would be if a person who thought they knew a group of friends was involved in a murder, then set out to blackmail one of the friends - could she, by stalking, somehow find out personal details about the entire group of women, then threaten them also? What methods would she be able to use to gain personal information about them? Would it be confined to stalking them?
Your story sounds interesting, and definitely possible. Stalkers, especially the ones who are very, very focused on their victim, can do a lot of things to gather personal info.
Most stalkers are male, a current/ex boyfriend/husband trying to keep the woman from leaving, or trying to get her back. Less frequent, but often more obsessed, a male stalker trying to make a women he loves love him, even if she doesn't know him. Also less frequent, a female stalker stalking either a man or a woman, trying to get their attention or trying to get revenge for some real or imagined action.
Here are some of the methods stalkers have used to get info about their target. Going through garbage at home or work. Stealing mail. Breaking into the home of victim's friends or family to look for address books, to find victim's address/phone. Pretending to be someone else, such as an old college friend calling victim's family (to get in touch with victim), or a realtor interested in the property just vacated by the victim (to find out where victim has moved), or a relative with a family emergency. They sometimes use other people to stalk for them ("stalking by proxy"), for example, getting a friend to try to get info about the victim. If the stalker has a friend who is a police officer, the police could run the victim's plates to get info about where she lives or any arrest records. A stalker might be able to contact the credit bureaus to get, not the victim's whole credit history, but just partial info which can include address.
If the victim is careful driving to and from work so she can't be followed, and has a post office box for mail to try to keep her home address secret, the stalker could wait for her outside the post office and follow her home from there, if she isn't careful. If the victim lives in an department complex with some security, perhaps posing as a delivery person for flowers or pizza could get the stalker inside the building.
If your story takes place after widespread use of the Internet, there are vast resources online for finding out about people. If a stalker knows, or can guess, passwords, they can login as their victim, and get lots of info that way. They can install a keystroke recorder in the victim's computer, and monitor not just passwords, but other online activities. I imagine that a stalker with this kind of access to their victim's computer could also tap into the victim's online calendar, to find out when/where she will be. See http://www.glr.com/stalk.html
or www.haltabuse.org for more info
Thanks for asking your questions, and good luck with your story. - Lyn