I don't have any definite answers, I'm afraid. But do have some thoughts.
What if the person who murdered this girl claims me as their next victim? What if I'm being stalked by someone I know.
Do you have an ex partner who's behaved in an obsessive way? Or a friend or colleague who's worried you with their behaviour? If not, then. I think the risk of a stalker is very, very low. Especially it being the same person who killed another woman. It's a big TV crime theme. Because it's scary. But real life is different. It's so much rarer.
How am I supposed to live knowing there might be someone out there plotting to kill me?
I think perhaps it's about assessing risk. Being alive comes with risks. Getting in a car. Walking to the shop. Eating a new food. Meeting new people. They all have potential hazards associated. But we try to work out what's likely and what's unlikely. Most people don't worry about a car crash every time they drive somewhere. Even though that's clearly a possibility on every journey. Likewise, unless I'm already seriously allergic to certain foods. It's unlikely I'll be afraid to try new things. In case I have a fatal reaction. The benefit vastly outweighs my perception of the risk.
Life starts to become difficult when risk assessments result in excessive limitations. So if you can find a neutral person to discuss the anxiety with. That might be really helpful. Family and friends aren't usually good at that. They want things to be OK. So may miss genuine warning signs. If you're able to talk to a counsellor, social worker or therapist. They can help you sort through what you know and what you fear. To work out what's reasonable. Putting a latch on your gate seems to make sense. Setting up CCTV cams that link to the police station doesn't seem to make sense. So getting some help in the midground of the response is useful. And they can also offer support if other people are either being dismissive or alarmist. Do you have any ideas on someone who might help in this way?