You live in texas.... get a firearm and keep it in your home. Problem solved
You have to determine if this was a one time thing or a fairly regular event in the area. Go drive through the neighborhood a few times late in the evening, that will give you an idea of what to expect(are their crackheads climbing trees at 2am, is there a random unattended baby standing in the yard at 11pm wearing nothing but a diaper). As for a double murders they are pretty common in the sense that even a really nice neighborhood will have one once in a while. In my last neighborhood, multiple $750k+ houses, upscale neighborhood, we had 2 double murders in a 10 year period. Well... Murder suicide but same difference really.
There was only like a 45% chance that a madman was living in the walls and murdered them, you shoulda kept the apartment.
It could be haunted and that can't be used to get out of a lease so think carefully.
Bad call, but we all make mistakes.