They said they thought they would have found the car sooner. I fail to see why that's a motive to conceal it until now, however.
I think there is a very plausible explanation as to why law enforcement would conceal a vehicle that may have been at the scene. It actually relates to what I personally think is the most likely scenario given what we do and don't know about this case.
I think that TB was hit by a vehicle, the occupant(s) of that vehicle panicked, and put him in the car. I don't claim that this is exactly the case, but it seems that with the information we have and the timing of release of certain information, this could be more likely than not.
For example:
1. The news has reported that when TB was initially found, investigators were unable to immediately determine a cause of death. It was not obvious what had killed him right away. If TB were hit by a vehicle, it may not necessarily result in obvious injuries to the outside of the body. Internal bleeding or a broken neck are not usually visible to the naked eye, but would be immediately apparent during an autopsy - and are injuries that would be consistent with homicidal violence. This could also explain a panic from the parties involved - if TB had internal bleeding but seemed otherwise okay, and then he suddenly took a turn for the worse - I could see a "dump" happening.
2. In the same respect, not releasing detailed information from the autopsy could be because of the nature of those injuries - it could indicate to a potential perpetrator that the police are looking for a vehicle - or maybe even the autopsy indicates that glass or paint fragments were found embedded in TB's skin. There is plenty of reason to want to withhold that type of information, even if it is frustrating to the public. And I am pretty sure that TB's family would be told the content of the autopsy.
3. Releasing the information about the vehicle now means they have more than likely been looking for this vehicle the whole time. Maybe they were hoping some evidence found on TB's body (if any, we don't know what, if anything, was found) could link a make or model. And it also gives the perpetrators the illusion they aren't being sought - what is the first thing you would do if your vehicle had been used in a crime? Dump it, sell it, get rid of it. Not releasing that information bought law enforcement a little time to try to identify the vehicle on their own.
4. The timing of the "dump." The car was seen at 7:35 pm. This would be over 12 hours from when TB was last seen, from my understanding. If he seemed okay, and then suddenly wasn't, that could explain the timing discrepancy.
Of course, I have no idea if any of this is true, and I don't have any info or knowledge to back it up other than the analysis posted above. I do know that car accidents don't necessarily leave "evidence" (like broken glass) all the time, but you would think that if there was an impact hard enough to break a neck or cause internal bleeding there would be some evidence of a crash. It is just an idea, and my own opinion. *shrug*
