Hayden Panettiere's Boyfriend Told Cops She Had History of Nitrous Oxide Abuse

Hayden Panettiere had a history of abusing nitrous oxide … according to what officials say her boyfriend, Brian Hickerson, told them after she died from a drug overdose.

In the coroner's report, obtained by TMZ, investigators say they sat down with Brian -- whose name is redacted in the report -- and claim he told them she had a long history of drug, alcohol, and nitrous oxide abuse.

Investigators say Brian also informed them that Hayden had recently gotten out of a drug rehab center in Malibu ... just a few weeks before she overdosed.

As we've reported ... Hayden passed away August 16 in Greenville, South Carolina, of an accidental overdose.

According to the coroner's report, she was found to have Fentanyl, Alprazolam (generic Xanax), a muscle relaxant called Methocarbamol, and Quetiapine, a drug used to treat bipolar disorder, schizophrenia and major depression, in her system when she died.

The report says Brian and his brother Zach Hickerson discovered her face down in a sitting position on a sofa bed with her legs crossed.

The Hickersons say they also noticed Hayden had turned deep purple as they tried but failed to wake her up. They gave her Narcan and then called 911.

The coroner's report also indicates her parents -- Skip Panettiere and Lesley Vogel -- fought over who should get some of the personal belongings the coroner removed from her body during the autopsy ... notably, several stud-type earrings.

Hayden's celebration of life was held last weekend ... the Hickersons and Lesley did not attend.

A source close to Hayden's mom Lesley denies she was not invited to the memorial, but admits she did not attend due to a family emergency.