Authorities named 48-year-old Jesus Salgado, who had been taken into custody and was in critical condition, as a person of interest.
Mr Warnke added that Mr Salgado had been talking to the police.
“There’s no words right now to describe the anger I feel and the senselessness of this incident,” he said.
“I said it earlier: There’s a special place in hell for this guy.”
Authorities have not yet established a motive for the kidnapping.
“We have a whole family wiped out and for what? We don’t know yet,” Mr Warnke said.
The family was taken from their business in Merced, located about 200km (125 miles) southeast of San Francisco in the San Joaquin Valley.
The sheriff added that the victims’ families had been notified about their deaths.
“We’re hoping that they can now at least have some kind of closure,” Mr Warnke said. “It’s not the closure we were hoping for; it’s not the closure they were hoping for.”
