At first, the police thought precisely what you probably do right now. Dude was a lawyer. He was bound to have enemies among the criminal element. Shit, he was supposed to finish a plea bargain against two violent drug dealers the very next day! Of course someone with a grudge grabbed him when he exited the courthouse late at night, forced him to drive around and mix-and-match his toll-paying methods in order to confuse the potential followers, and finally found a quiet place to torture-murder him. We've seen movies. That's how these things work.
On the other hand, the investigation uncovered that Luna was, partly unbeknownst to his family, pretty heavily in debt, and that he had profiles on multiple internet dating sites. Also, he was totally seen during the trip. The gas station attendant he bought gas and beverages from didn't see anyone else in his car, and attested that he behaved completely normally. Whatever the dude was doing, he was likely doing it voluntarily. So ... maybe the guilt of his apparent secret life got to him and he went on a midnight drive to clear his head, only to have the dreaded 2 a.m. thoughts eventually take him over and, as it were, under? Or maybe he was trying to stage a suicide or a kidnapping and went too far?
"Juuuust a quick 36 stabs to convince people I'm not playing aroun-"
Pauli's Favorite Theory:
At first, my gut instinct was to go with the "ridiculously elaborate suicide" theory, but ... no, man. This dude was totally murdered. Sure, some say that his penknife wounds could have been largely "hesitation wounds" common to blade-related suicides. However, this has been debunked by the mortician who took care of Luna's body for the funeral, who said that his wounds were the worst she had ever seen. We're talking "shredded hands, slashed scrotum, slit throat, and stab wounds in the back" stuff here. Even without back-stabbery and the fact that Luna's corpse was the worst thing a freaking mortician had seen, I refuse to believe that a dude trying to commit a quiet desperation suicide would incorporate scrotum-slashing into the act.
Besides, Luna had left his cell phone and glasses, which he needed to drive, on his desk before he left. Also, there was a pool of blood on the back seat of his car, which would seemingly indicate that he was lying in the back ... and someone else was driving the car. Which means the gas station attendant never saw Luna, but his murderer. Specifically, someone else that they could still later identify as him. This leaves us but one choice: He was murdered by his evil twin from an alternate dimension. I bet the FBI has also arrived at that theory, which is why they keep giving contradictory statements about the case.
"I'm sorry, sir. It's just that Agent Mulder keeps hijacking the microphone."