Hi. I'm a long time lurker here, and now first time poster. I read this thread this morning and thought it wouldn't hurt to add my thoughts to the discussion.
I feel very strongly that the "personal emergency" phone call is a key detail to solving this mystery. It needs to be weighed heavily in any theory about what happened. It is an integral piece of the puzzle, and I can't imagine any break in the case that doesn't directly tie in with that.
I know some of the things I'll say will be very basic, obvious, or even ridiculous, but I want to really break down the logic behind what's able to be inferred from the information available. That way it's easier to notice any inconsistencies or leaps. I don't at all mean for any of this to come across in a condescending way if that's the case!

eace: :angel:
Mark made the phone call
If Mark made the phone call, he was obviously dealing with someone he knew. I can't think of any potential "personal emergencies" he would call work about where he isn't either dealing with someone he knows, or taking himself to the hospital (which doesn't seem to be the case).
Furthermore, the fact that he was calling out of work says a lot about what he anticipated; whatever this "personal emergency" was, he only needed to call out of work for it. He wasn't afraid for his life, so whoever the person was, Mark did not know them to be violent or dangerous. He didn't call his family or the police. This is consistent with the speculation that the person who did this didn't have a criminal past or future after killing Mark. Was Mark naive, or did the situation escalate? Was the "emergency" somehow bigger than he was aware of?
How did Mark find out about this personal emergency? There are obviously a number of possibilities, but I imagine could have been a phone call. Were his phone records investigated? Had he spoken to anyone, probably RIGHT before he called work? The 4th of July was a Sunday; what was his work schedule like? If he the information he learned that constituted a personal emergency didn't come via telephone, it probably came to him in person. Was he at work the night before, or was he at The Eagle Bar? I am leaning toward the phone, though.
(* I just found this article, has it been posted?
http://koin.com/2014/07/02/united-airlines-employee-presumed-dead/)
Someone who isn't Mark made the phone call
After I looked over everything I wrote, I noticed I had completely glossed over a very important piece of information which was that Mark was seen the day after he called out of work. Oops! I'll leave the following two sections in my post, though, for the off chance that the sighting was fake/incorrect (there is a discrepancy about his last sighting, after all):
The phone call also might NOT have been made by Mark. Again, I have no idea how likely that is, but it's possible, so I want to talk about that too.
If someone besides Mark made the phone call, they were pretending to be Mark (a personal emergency phone call in third person surely would have been mentioned by whoever reported the call in the first place(?)). The perpetrator would have to know Mark well enough to 1) know he was supposed to work, 2) know where he worked, 3) know the phone number. Again, either way you look at it, Mark knew this person, and probably very well. Unless some combination of a phone book and planner were used, which isn't impossible.
There was no phone call
The third possibility, which is a weird one, is that the call didn't happen. This would imply that his boss or whoever he would normally call is involved. If his phone records were never checked, though, it could have happened. I don't think it did, but I wanted to include it either way.
For argument's sake, there is a (very slim, imo) chance that the phone call was unrelated. If that's the case, I can't even imagine what took place.
The news article did have one line that sticks out to me as odd, and I'd like to hear others' opinions:
"Crime scene photos showed
biological evidence in Dribin's house on Northeast 137th Avenue. All over the walls was evidence of blood spatter that investigators said appeared someone had cleaned up."
"Biological evidence?" Was the author just using a synonym for blood, or was something else found? I know there's no way of knowing, but I am mainly curious if the word choice caught anyone else's attention. To me, it felt like it could have been a polite way of omitting more "scandalous" details. However, I'm sure that other posters here are much more well-versed than myself with this sort of article, and it might be very normal. There was unidentified DNA at the scene, correct? Was it blood, or "biological evidence?" And what kind of death causes blood spatter on the walls? It seems either way to be too extreme for a dangerous-but-consensual act gone wrong.
Mark's car
This is the most confusing part of the story to me, but also probably as important as the phone call. Why would someone take Mark's car, only to abandon it in the same town? It was left in a place where it would obviously be found, and any evidence accidentally created and left in the car would be immediately linked to the case. Did the killer NEED to take his car to get away?
Mark lived about a half hour away from The Eagle Tavern by car, about an hour and a half away by public transportation (today, at least), and a 3 hour walk.
Mark's car was found about a half hour away from his home.
Mark's car was found a 17 minute drive or an hour and a half walk from The Eagle Tavern.
If the killer was able to get home from where the car was abandoned, they probably lived in the area; this doesn't necessarily mean anything, but it's an additional piece of evidence that Mark knew his killer.
Where did the killer go after abandoning the car? They could have 1) lived close by, 2) gone back to the Eagle Tavern to pick up their own car, 3) used public transportation.
The Eagle Tavern would have been active at night. If Mark was sighted there, then he was alive the night of Saturday, July 3rd. If he took someone back home with him in his own car, it would have been too late for that person to take public transportation home. This would explain why they had no choice but to steal the SUV. Can anyone think of any other explanation for what happened to his vehicle?
The community
It's very, very difficult for me to believe that there aren't people who know what happened to Mark. I can't help but wonder what could be important enough that they're afraid or unwilling to talk. There is so much reason to believe that whoever was behind this murder was a member of the same, specific community that Mark was a part of. Was he really out socializing the night after he called out of work for a personal emergency, and no one in the bar he frequented enough to be recognized knows what happened? He was known at The Eagle Tavern, but he didn't say goodbye to anyone? No one saw who he left with? Or did he, in fact, leave alone? Did someone expect him to be there, and somehow enter his vehicle unbeknownst to Mark? Even if that's the case, how did every single one of his past lovers or partners, whether there be 1, 2, 5, or 10 of them out there, manage not to be even a person of interest? I wonder who they were, and if they were ever actually questioned. It would be unfortunate (and completely irresponsible), but perhaps the detective(s) at the time were homophobic and uncomfortable entering a gay bar to investigate. There are so many questions!
A possible motive for a scorned lover (and I say this with complete respect and compassion, and not a shred of judgement, as I have beloved friends and family members, just like Mark, who have dealt with this issue); could Mark have been involved with someone who contracted an STD such as HIV? A former partner could have been diagnosed, and blamed Mark. They could have even simply informed him. That alone would be reason enough to call out of work. If there were no former boyfriends mentioned or even known to his family, it's possible that Mark hadn't been in any long-term, committed relationships. If that was the case, a betrayed lover would be unlikely. On the other hand, someone with no history of violence who was just given (what in 1999 could have felt like) a death sentence may have been driven to murder, especially if they thought they (and the victim, for that matter) would soon be dead anyway. If the culprit passed away or was terminally ill, it might explain why those who knew what happened, assuming they existed, failed to come forward.
One last thing:
Is the "White Eagle" Tavern separate from The Eagle Tavern?
http://www.ghostsandcritters.com/oregonghosts.html
While I'm not into paranormal, this website mentions a "haunted" bar in Portland called the White Eagle which experienced "many strange events",
specifically in the early weeks of July 1999.
Thank you for taking the time to read this. As I mentioned above, I learned new information I had previously missed after I had begun writing this, so hopefully it still holds up. Hoping to hear what others think, and looking forward to a resolution to this case.