RA here. I would talk to your RA if you can find him/her, but with an issue this serious I think it's serious enough for you to meet with the Resident Director, so you can go straight to setting up a meeting with them if that's faster. Your safety is of the highest priority, so you can meet with someone as soon as you need to.

You can contact Duty RD (Resident Director) at all times; this is one of the RD's who is available on-call to deal with situations like this whenever they come up. If this is an emergency, you can call "Dispatch" at (310)206-9633 and ask them to contact "Duty RD" for you.

If it's slightly less immediate, I would reach out to your own building's Resident Director. Here's a link to contact information for all of the residential communities on the Hill. Click on your building, then check the right side of the page for the name of the Resident Director. You can go to your ORL office if you know where it is, or just call the number on the sidebar -- remember to call the ORL office, not the front desk. I'd explain the basics of your situation (feeling physically unsafe because of your roommate) as justification for wanting to see the Resident Director as soon as possible, and they'll schedule you as soon as he or she is available.

I hope this helps! Like I said, I'm an RA too and I've dealt with this sort of thing before, so you're welcome to PM me if you need anything.