Some thoughts about the car and the remains.
After looking at the map and doing some routes, I think he probably left Ingrid's home and tried to avoid being on the freeway. If he did this, he could take Rainier Ave. or MLK Way all the way to the place where the partial remains were found. From there, it is kind of a straight shot to Belltown - though not particularly close, he could follow his nose and look for a parking place. If it was early in the morning, I do know that Belltown is a place where cars are often parked overnight and ticketed, rather than towed. Being an area with a large amount of bars, there is an expectation that a car may be left overnight and if drunk partiers have to worry about a car being towed, they might be less likely to leave it. I have been the recipient of one of these tickets in my younger days
I think if he was thinking of a place to dump a car, that that might buy him a bit of time. I also think he may have called his ex girlfriend, said that he got drunk and possibly in a fight and passed out in Belltown and could she come pick him up. This explanation would explain if there was blood and his scrapes and cuts. Though I think he could not have been wearing clothes or the same clothes as when the crime was committed.
I tried to think of this as a drugged or drunk killer might. If something happened out of rash thinking (she refused sex, felt weird when he came on too strong, etc) he may have killed her in a rage. In an irrational and impaired state, parts of a body might seem easier to get out to a car and dispose of then a body. Maybe it was a case of him rationalizing that he had to do what he had to do.
While I see that he could make some effort to cover it up, I am not convinced that this was pre planned or well thought out. He made no attempt to cover his tracks ahead of time and a sloppy attempt to do so after the crime.
All my opinion, of course.