Vancouver police are probing the circumstances of the Glee star's death and an autopsy will take place on Monday to determine the official cause and manner of death.
Crucial to post-mortem examination: A toxicology report that will screen for drugs in the the actor's body. Medical examiners will also seek to determine if he died of natural causes or if any disease or injury may have been present.
However, toxicology results could take weeks, a law enforcement source said.
"The exact nature of those examinations will depend on investigative findings within the next day or two as information is gathered from medical records and discussions with family take place," British Columbia's chief coroner, Lisa Lapointe, said.
Monteith's abuse of drugs and other substances in the past will spur an investigation into his behavior over the final weeks, a source divulged.
Law enforcement will also look at what interaction he had with friends and Lea Michele, his Glee co-star and real-life girlfriend, in the days before his death at a five-star Vancouver hotel on Saturday, the source added.
"In situations where the victim had a past like he did, authorities will always look at whether the death could be linked to drug use," the insider said.
Monteith checked into a rehabilitation clinic in March -- his second such stint. He previously explained that his drug use consisted of "Anything and everything, as much as possible."
Detectives have already interviewed everyone who was with Monteith, who played Finn Hudson in the hit FOX television series, during the night before his death.
They've already established foul play was not involved and that he died alone in the 21st floor room of the Vancouver Fairmont Pacific Rim Hotel, where his body was discovered by hotel staff.
Investigators have not said publicly what they found in the room but it's understood they would have conducted a top-to-bottom search of the room.
"For the most part, it has been turned to the Coroner's Office who will be determining the next steps with respect to establishing cause of death," Const. Brian Montague said late Sunday.
A Glee production source told Radar: "The cast, like everyone else, just wants answers. Wherever the facts lead, they just want answers."
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