Story highlights A family member discovered the four bodies, authorities said

All died from gunshot wounds

Authorities are interviewing family members

Four relatives were found dead in what is believed to be a triple murder-suicide in northwestern Ohio, authorities said Thursday night.

A family member discovered the four -- Robert Garza Sr., his wife, Christine Garza, daughter Zoila Garza and granddaughter Rebecca Garza while checking in on them, the Defiance County Sheriff's Office said in a statement.

"We believe that Robert is the perpetrator of the crime and he shot the other three family members and then took his own life," Sheriff David J. Westrick told CNN affiliate WTOL

An investigation is under way. Other family members are being interviewed by authorities.

Westrick said Robert Garza had some "health issues," but wouldn't elaborate.