That is the basic question being asked by the family of Anthony Banta Jr.
The 22-year-old was shot to death early Thursday morning by Walnut Creek police officers who responded to a 9-1-1 call about a loud disturbance at the Creekside Drive apartment where Banta lived.
Family members are distraught and perplexed.
What, they ask, caused Banta to wake up screaming in the middle of the night and attack his roommate?
Why, they ask, did police use lethal force when Banta was armed with only a knife?
"We are devastated. Our hearts have been ripped out," said Brett Grainger, Banta's grandfather.
The officers involved have been placed on administrative leave while the incident is investigated by the Contra Costa County District Attorney's office.
The coroner's office completed an autopsy Friday, but a spokesman said findings won't be released for several weeks.
Grainger, whose daughter is Banta's mother, said Banta had cooked dinner for his roommate and the roommate's girlfriend on Wednesday evening.
Nothing seemed unusual, Grainger said, until Banta woke up screaming in the middle of the night. Grainger said Banta didn't know who he was and started choking his roommate when the roommate tried to calm him down.
Grainger said the roommate's girlfriend called 9-1-1. Police say they received that call about 3:15 a.m. and could hear someone yelling in the background.
Officers arrived minutes later. Grainger said Banta picked up a knife when police came into the apartment. The officers yelled for him to put down the weapon. When Banta didn't, Grainger said they shot him.
"Did they have to use lethal force?" asked Grainger. "Could they have used a taser or thrown a table or chair against the wall and subdued him? No one in the world deserves to die like this."
At a press conference Thursday morning, Walnut Creek Police Capt. Tim Schultz said the officers were concerned for their safety when they fired the shots.
On Friday afternoon, Walnut Creek Police Chief Joel Bryden said his department wouldn't comment further at this time due to the ongoing investigation. He said they will have more to say after the investigation is completed sometime next week.
Grainger said the family is still trying to sort out what happened early Thursday morning.
Grainger said his grandson was the "sweetest, kindest person who ever walked the face of the Earth."
He said the family believes Banta must had some kind of mental breakdown or possibly a brain tumor that caused him to act so out of character.
Grainger said his grandson did not use drugs and had no criminal record.
"He was a loving, caring individual who wouldn't hurt a flea," said Grainger.
Banta spent his early years in the Paradise area outside of Chico, where Grainger still lives. His family eventually moved to Yuba City. Banta graduated a few years ago from Yuba City High School.
He went to beauty school and was working as a hairdresser at Salon Amour on Newell Avenue in Walnut Creek. Grainger said he loved his work and was quite good at it.
"He was going places," Grainger said.
A recording on the salon's phone Friday afternoon said the business was closed.
Banta's mother is a registered nurse in Yuba City. Banta has a twin brother, Ashton, who is in the Air Force. Grainger said Ashton is flying back from Germany to be with the family.
Banta also has two younger sisters, ages 18 and 13.
Mandy Grainger, Banta's aunt, said her two children, ages 13 and 12, are having trouble understanding what has happened.
"All they know is he's gone," she said.
Grainger said she is still in shock over her nephew's death.
"I'm numb and I'm operating on very little sleep," she said.