HIPPA applies only to specified entities(see https://www.cms.gov/Regulations-and-Guidance/Administrative-Simplification/HIPAA-ACA/AreYouaCoveredEntity.html); including Health Plans, Health Care Providers, Clearinghouses, and "Business Associates".
Autopsy and toxicology records are the output not of a medical practice but of the coroner's office. The coroner is not* a health care professional; rather they are a law-enforcement official, and law enforcement are not constrained by HIPPA. Law enforcement records are often part of the public record, especially when they are attached to a court case.
The office of a coroner is empowered and charged with recording deaths in their jurisdictions, and determining cause of death for violent or suspicious deaths. In some jurisdictions, they have the power to instigate investigations. They often do this by overseeing (or, generally, in smaller jurisdictions, acting as) medical examiners and/or forensic pathologists.
*It is more proper to say that the coroner is not inherently a health care professional. Often, coroners may hold medical degrees. In some small (and often poor) counties, a/the local doctor does double duty. In others, the office of the coroner is combined into the office of the sheriff, and the positions are sometimes even merged into one person. In larger (and often wealthy) counties, the coroner may be a purely organizational and administrative position.