Fifty-two-year-old Hayashi candidly said he takes the blame for the terrible accident and for not getting rid of the family pit bulls when he should have. But he says he always supervised the dogs around his grandchildren.
"The last time I saw him was the day before and he gave me a hug," Hayashi said.
Through tears, Hayashi recounted some of his last memories with his grandson Jacob Bisbee before he was mauled to death by three of the family's five pit bulls -- family dogs he now considers killers.
"It's like, if somebody murdered somebody, you hate that person; it's the way I feel about dogs right now," Hayashi said.
Contra Costa County Animal Services euthanized all five dogs Thursday afternoon.
Police say Bisbee was attacked at his home on Trail Creek Court when he wandered into the garage where three of the dogs were. Hayashi was not home at the time.
"My wife found Jacob, the dogs weren't on him anymore, like they finished the act already," Hayashi said.
Bisbee's grandmother, 4-year-old brother and 19-year-old uncle were all home. Nobody else was hurt.
Hayashi says he is still wondering how his step-grandson even got into the garage.
"Jacob's never, ever gone downstairs to the garage," Hayashi said. "I don't, we thought, me and my wife were talking about it yesterday, we both thought that we dead-bolted the top lock."
Hayashi says he always monitored the dogs around the children.
"Four of the five dogs have come in contact with Jacob and his brother Jeremy many times, and they were very gentle," he said.
But Hayashi also admits that at least one of the five pit bulls had been aggressive in the past.
"There were definite signs," he said.
One dog had attacked and killed the family's Chihuahua, but Hayashi thought it was just aggression between animals, so he decided to keep all the pits bulls.
"If I knew this would have happened, I would have destroyed those dogs a long time ago," Hayashi said.
Hayashi says he never wants to own a dog again.
Hayashi will be charged with felony child endangerment and possession of a mischievous animal that resulted in death or great bodily injury. He is being held on $120,000 bail.