The 22-year-old man accused of trying to assassinate Representative Gabrielle Giffords in a deadly shooting rampage wrote “Die, bitch” in a note found at his home, a sheriff’s official said.
Investigators believe Jared Loughner’s handwritten message was a reference to Ms Giffords, Pima County Chief Rick Kastigar said.
It was found in a safe alongside other ones, including “I planned ahead,” “My assassination” and the name “Giffords”.
Authorities also revealed other new information about the hours leading up to the Saturday shooting that killed six people and injured 14 others, including Ms Giffords.
That morning, Loughner’s father saw him take a black bag out of a car trunk, Sheriff Clarence Dupnik said.
The father approached Loughner, and he mumbled something and took off running, Mr Dupnik said. The father got in his truck and chased his son as he fled on foot.
“The bag is very important to us,” said Captain Chris Nanos, head of the Pima County Sheriff’s Department’s criminal investigations division.
“What was in that bag and is there any relevance?”
“What if he wrote a note that says, ’Hey, I’m going to go do these things and I know it’s wrong but I’m still going to do them’,” Mr Nanos said. “That’d be a pretty good piece of evidence.”
Loughner took a taxi cab to the supermarket where the three-term Democrat was holding a meeting to hear the concerns of her constituents, authorities said earlier. Among those killed were a federal judge and a nine-year-old girl.
Meanwhile, several hundred mourners filled a Tucson church for a public Mass to remember the dead and pray for the injured.
As people filed in, nine young girls sang Amazing Grace. The youngest victim of the attack, nine-year-old Christina Taylor Green, was a member of that choir.
Today, President Barack Obama will visit Arizona and give a speech honouring those killed.
Loughner’s parents, silent and holed up in their home since the shooting spree, apologised.
“There are no words that can possibly express how we feel,” Randy and Amy Loughner wrote in a statement handed to reporters waiting outside their house.
“We wish that there were, so we could make you feel better. We don’t understand why this happened. We care very deeply about the victims and their families. We are so very sorry for their loss.”
Meanwhile, the southern Arizona city shattered by the rampage prepared for an evening memorial service and a visit from Mr Obama.
The apparent target of the attack, Ms Giffords, 40, was able to breathe on her own at an intensive care unit here, another hopeful sign of her progress and doctors said she will likely survive.
Doctors emphasised, however, she is in for a long recovery.
“She has a 101% chance of surviving,” said trauma chief Dr Peter Rhee said. “She will not die.”
She also can breathe on her own but still has a breathing tube in place as a precaution, said her neurosurgeon Dr Michael Lemole.
In their briefing, doctors also reversed themselves in describing the path of the bullet. They now believe she was shot in the forehead, with the bullet traveling the length of the left side of the brain, exiting the back.
Doctors previously thought she had been shot in the back of the head. They came to the new conclusion after reviewing X-rays and brain scans and consulting with two outside physicians with experience treating combat victims.