Hermann's 13-year-old daughter, Sarah Maynard, was found bound and gagged, but alive, in a basement of a home about 15 miles from where the bodies were discovered.
Knox County Sheriff David Barber said investigators were led to the bodies by unemployed tree-trimmer Matthew Hoffman, who is accused of kidnapping Maynard and keeping her for nearly four days in the basement of his home in Mount Vernon.
"We were optimistic a few days ago that maybe there was a remote chance that these folks were possibly still alive," Barber said. "This is a homicide investigation now."
The sheriff said the three were killed in Herrmann's home in Howard, though he did not say how.
Barber also said Hoffman gave investigators information through his attorneys that led them to the bodies, which were removed after part of the tree was cut away.
At a vigil in Howard, Ohio, Thursday night, mourners lit candles and sang hymns to remember the three killed.
Hoffman, 30, who spent six years in a Colorado prison, is charged with kidnapping Maynard. He is also the only suspect in the killings, Barber said.
The Associated Press contributed to this report.