I've been wondering that too. Left to right, we know Maddie had the white car, Kaylee the rover, the blue car belonged to X. I'm not sure if the jeep belongs to E but, after the frat party, he could have easily walked with X to her house or they drove back in her car.
Since the video of LE casually removing something (as opposed to searching) from the red jeep, it leads me to believe it belongs to one of the surviving roommates.
So, the SUV, I'm guessing from the below picture full of police cars, is an unmarked police vehicle staying there to guard the house and crime scene. IMO/MOO
Link to SUV