India, Sept. 14 -- Actress Hayden Panettiere died last month after taking a single pill believed to have been oxycodone laced with fentanyl, according to multiple law enforcement sources cited in a TMZ report published Monday, as investigators work to trace the fatal dose back to the dealer who supplied it.

Panettiere, best known for her role in the television series "Heroes" and for "Scream 4," was 36 when she died on 16 August at an apartment complex in Greenville, days before what would have been her 37th birthday. Her official cause of death has not yet been released, and toxicology results are not expected for several weeks.

Hayden Panettiere: What Do Investigators Believe Killed Hayden Panettiere?

Sources connected to the case, c...