As for why the police have been slow to release information to the public, I have two ideas:
1) They didn't want to release the cause of death, or any other details, until the memorial service was over, out of respect for family and friends.
2) Keeping information secret would aid in their investigation. Releasing details would give information to the suspect(s), would intimidate potential witnesses, would reveal too much about what the police knew.
As for the cause of death, the overdose theory makes the most sense, although from what I can gather, Halle didn't use heroin, but instead a lot Xanax, weed, and alcohol. I guess when I think about overdoses, I usually automatically assume it's heroin. I know you can overdose on a lot of other things other than heroin, and that just because in the past Halle didn't do heroin, doesn't mean that she didn't start. I know some people very close to her did. So, maybe an overdose. Maybe some of that awful fentanyl-laced heroin that's killing a lot of people. Who knows.
I also think that the "she knew too much" theory makes sense. From what I can see, Halle hung out with some pretty sketchy characters. Drug dealers, gang members, etc. Though she often defended them, it is possible that she happened upon some information that certain parties might not want her to know. Or that her loyalty was questioned.
Another theory I have is that she left that party at Joslen Motor Lodge that she may or may not have been at on Saturday night, wandered a bit, and was murdered by a random who happened upon her, a crime of opportunity.