Photos reveal the actor, who died on July 13 of a lethal mixed drug toxicity of heroin and alcohol, with possible injection sites on his arm in Los Angeles on July 9, 2012.
A month later, Monteith was snapped in Soho, New York, with similar markings.
The fact that Monteith had a number of "track marks" on his body would have made it clear to anyone around him that he had a drug problem.
Friends, including Michele, 26, convinced him to enter rehab in April, though it's said his girlfriend "didn't know" that he had relapsed with heroin following what was to become his second stint in treatment.
On Tuesday, the British Columbia coroner confirmed that Monteith, aged 31, died of a drug overdose.
"It should be noted that at this point there is no evidence to suggest Mr. Monteith's death was anything other than a most-tragic accident," their report said.
"The BC Coroners Service will not be providing any further details or responding to inquiries concerning the circumstances of Mr. Monteith's death until the full investigation has concluded."
"There were indications in the room that this was a drug overdose," Vancouver Police Department media relations officer Brian Montague added. "We're not providing exactly what we found at the scene. Anything that was found at the scene would be evidence."