Hayashi, 53, has pleaded not guilty to charges of child abuse, owning a vicious animal and an enhancement alleging that he allowed his step-grandson, Jacob Bisbee, to be in a situation that resulted in his death.
The attack happened the morning of July 22, 2010, at Hayashi's home at 1785 Trailcreek Court in Concord, where Jacob, his older brother and their father lived with Hayashi, his wife and their two teenage sons.
Hayashi also had five pit bull mix dogs, which he kept in the backyard and the garage.
Knox argued that Hayashi knew the dogs were aggressive, particularly toward the children, and had not taken adequate steps to protect the children from the dogs.
She argued that he acted with conscious disregard to human life by keeping the dogs in the home and failing to prevent the attack and therefore should be ordered to stand trial on charges of second-degree murder.
Hayashi's attorney Pamela Lauser, however, argued that there was no evidence that Hayashi was responsible for the children when the attack happened or that he knew that the dogs were vicious.
She objected to Knox's request to have a murder charge added and asked the judge to dismiss the charges.
On the morning of the attack, Jacob's father, Michael Bisbee, left at about 5:30 a.m. to go to work.
Hayashi left with his son a couple hours later to go play tennis, leaving Jacob, his 4-year-old brother and Hayashi's wife asleep upstairs, Hayashi allegedly told Concord police Detective Greg Rodriguez.
Downstairs, three pit bulls were in the garage and two were in the backyard.
Hayashi allegedly told Rodriguez that he usually locked the door from the house to the garage but that he had not locked it that morning, Rodriguez said.
He also admitted that he did not wake up his wife, who worked a late shift and usually slept late, before he left.
At about 8:45 a.m., Jacob went into the garage and was attacked by the three dogs inside. The two dogs in the yard were not part of the attack, police said.
Concord police Officer Jim Nielsen testified that when he arrived at the house that morning, he found Hayashi's wife giving CPR to a toddler. He said he took over CPR until paramedics arrived, but never saw any sign that Jacob was alive.
Jacob was taken to John Muir Medical Center, where he was pronounced dead.
The Contra Costa County coroner's office found that he died from skull fractures and severe bleeding from multiple dog bites.
Concord police Forensics Specialist Linda Damarco testified that she witnessed animal autopsies, known as necropsies, of the dogs and watched as a piece of Jacob's shirt and some buttons were removed from the stomach of one dog and hair, believed to be from Jacob's head, was removed from the stomach of another dog.
In a jailhouse interview the day after the attack, Hayashi admitted that he knew one of his dogs, "Kiwi," was aggressive and said that the dogs had killed a pet Chihuahua about a year earlier.
Knox, however, said that the dogs had also killed an Akita -- a large dog that can weigh 70 to 100 pounds -- and a pet parrot, and had showed previous signs of aggression toward Jacob and his brother.
Hayashi has said the dogs were supposed to be family pets and were not bred for fighting.
Contra Costa Animal Services Lt. Joseph DeCosta, however, said that when he arrived at the house shortly after the attack on Jacob the dogs appeared to be acting as a pack and were in a state of frenzy as they tried to attack his fellow animal control officers.
The three dogs in the garage were throwing themselves against the door, DeCosta said.
"They were physically trying to chew through the door to get to the officers," he said.
The two dogs in the backyard were throwing themselves up against a sliding glass door that led into the living room, he said.
"I believed the dogs to be in a state of frenzy," DeCosta said.
Concord police Cpl. Joseph Higby testified that there was a lock and a dead bolt on the door from the house to the garage, but no child safety mechanisms were in place. The doorknob was only 3 feet from the ground with the dead bolt about 6 inches above that.
Rodriguez testified that he interviewed Hayashi at the hospital and then again at the police station.
During his initial interview at the hospital, Hayashi allegedly told Rodriguez his wife had asked him to get rid of the dogs because it was dangerous to have them around young children.
"I know the animals have aggressive tendencies toward people and other animals," Rodriguez said Hayashi told him.
Hayashi allegedly told Rodriguez that Kiwi was particularly aggressive and was not allowed around the children.
Rodriguez said Hayashi told him that in the week before the attack, Jacob had become interested in the dogs and would stare at them through the sliding glass door in the living room. When Kiwi saw him, he would allegedly bark at him aggressively and charge the door.
During another incident, Hayashi said he was holding Jacob and Kiwi jumped up and nipped Jacob, Rodriguez said.
Hayashi allegedly admitted to Rodriguez that he knew the dogs were aggressive and that was why he tried to keep them away from the children.
Hayashi's wife, Leticia Hayashi, who testified for the defense, claimed that Jacob's father left the house at 5:30 a.m. every day without discussing childcare arrangements with anyone.
She said she worked a late shift at work, so her husband would usually take care of Jacob and his brother in the mornings when their father "abandoned them".
She said she had asked her husband to get rid of the dogs because she was tired of cleaning up after them, not because they were vicious.
"They bark, but they're not vicious," Leticia Hayashi said.
She claimed she had never seen the dogs behave aggressively toward anyone in the home.
She denied telling a police officer at the hospital that she knew something like this would happen and that it was only a matter of time.
She denied telling the officer that Jacob and his brother could reach the locks on the garage door and that she had asked her husband to put the locks higher up so they would not be able to reach them.
She claimed that Bisbee moved into their house without permission and would often leave children in the house without telling anyone.
Lauser also called Bisbee to testify, but he did not show up. The purpose of the preliminary hearing is to allow a judge to decide whether there is enough evidence to bring the case to trial.
Contra Costa County Superior Court Judge Clare Maier heard the case today and is expected to make her ruling Thursday morning.