A California sheriff has scheduled a news conference to announce the causes of death of a Northern California family and their dog who were found in a remote hiking area in a case that has baffled authorities. 

Mariposa County Sheriff Jeremy Briese will hold the news conference Thursday to discuss the mysterious deaths of John Gerrish, his wife, Ellen Chung, their 1-year-old daughter, Miju, and their dog.

The family went hiking on a trail close to the Merced River in the Sierra National Forest, where they were found dead Aug. 17 after a family friend reported them missing. 

Mariposa County Sheriff’s investigators have worked with toxicologists, environmental specialists, the FBI and other experts. They have already ruled out the causes being related to a gun or any other weapon, extreme heat, a lightning strike, carbon monoxide, carbon dioxide, cyanide exposure, illegal drugs, alcohol or suicide.

One early theory that has not been ruled out is whether high levels of toxic algae detected in the Merced River played a role. Investigators have results from water samples taken in the area but were still waiting for other test results to help determine if the levels were high enough to kill them. 

The deaths led the Bureau of Land Management to close campgrounds and recreation areas along 28 miles of the river, between the towns of Briceburg and Bagby, when water samples downstream from where the family died showed high levels of toxic algae.