what i did was run into the observatory (dont just shut the doors he can break them down. learned that the hard way)... if you run towards the center and up some stairs i think there was a power switch.. apparently turning it on opens some doors you can close on him which kills him if timed right (i think thats p much the only way to kill him and get extra exp)

but what i did was run thru the building as it chased me and eventually i got far enough ahead and crouched behind a wall.. then he just stormed around outside for the remaining 3 minutes, but he can burst thru the walls or doors or something so i'd see him pass by sometimes