I don't believe that scenario is ruled out completely. Depending on the evidence they have gathered, the possibility may still exist that she was unknowingly given drugs by someone which resulted in her death. There have also been cases where someone has died from a voluntarily ingested drug and the person supplying the drug has been charged with the death. So I think a drug induced death is still a very real possibility here, although I doubt Celina would have knowingly taken drugs.
Yes there have been many cases of people knowingly or willingly taking drugs, overdosing and dying, but those cases are classified as an accidental death, not homicide.
Since Celina's case has been ruled a homicide I think we can rule out that Celina was "willingly" taking drugs with someone at the time of her death and then the person disposed of her body in a panic when she died.
Supplying or distributing drugs to someone that willingly takes the drugs results in their death is a crime, but it is not murder or homicide. So since Celina's COD is homicide someone would have to be charged with murder or manslaughter.
Now if someone forcefully injected Celina with drugs then that would be considered a homicide, but since no one seems to be talking I don't think that is the case or we would have seen an arrest by know. In other words how would the ME be able to determine if Celina was given drugs against her will to know that this was a homicide.
If Celina had some kind of poison in her system than that would tend to lead to homicide, but killing someone with poison takes time and thought. It is not just a spur of the moment thing you decide to do at 9 PM. Trying to inject someone would likely create a struggle and the others in the house would have been alerted to something going on. You don't just come at someone with a needle to inject them with a poison (or a drug for that matter) and they don't scream or try and get away. Forcing someone to drink a poison like drain cleaner in a lethal dose would likely have the person running around the house for some time screaming in pain before they died. That would surly wake someone up in the house.
I'm sure their are drugs or poisons that someone could be given that would cause a death unsuspecting to the victim, but again that would take a lot of thought and planning. Something I don't think this case had. If someone took the time to plan on how to kill Celina with a poison or drug unbeknownst to her, they wouldn't have wrapped her in a "blue" blanket and dumped her in the river were she would likely be found. They would have planned a spot where she was likely never to be found.
JMO
Here is a recent case of two people being charged with supplying (distribution) drugs to someone that resulted in their death. Note that neither person was charged with murder. The lady in the case was even the one that injected the drug into the man that died. How did LE know that? Because one of them talked. Ironically she was the one that was acquitted of the crime, likely because she wasn't the one that actually purchased the drugs.
http://www.stltoday.com/news/local/...cle_f78f04c2-d027-11e0-9386-001a4bcf6878.html
http://www.stltoday.com/news/local/...0b3-11e0-a022-0019bb30f31a.html#ixzz1YWHXbqUy