Investigators say that the attacker who opened fire on pupils as they were praying at a church in Minneapolis was "obsessed with the idea of killing children".
Robin Westman, who killed two children and injured 18 others, did not seem to have any specific motive, according to Minneapolis Police Chief Brian O'Hara.
The attacker "appeared to hate all of us", the chief said on Thursday, adding: "More than anything, the shooter wanted to kill children".
The murdered children have been identified by family as Fletcher Merkel, eight, and Harper Moyski, 10.
"Yesterday, a coward decided to take our eight-year-old son Fletcher away from us," his father, Jesse Merkel, told reporters.
"We will never be allowed to hold him, talk to him, play with him and watch him grow into the wonderful young man he was on the path to becoming," he said.
"Fletcher loved his family, friends, fishing, cooking and any sport that he was allowed to play."
"Please remember Fletcher for the person he was and not the act that ended his life," he continued, choking back tears.
"Give your kids an extra hug and kiss today. We love you, Fletcher. You'll always be with us."
The parents of Harper Moyski, Michael Moyski and Jackie Flavin, said in a statement that their daughter "was a bright, joyful, and deeply loved 10-year-old whose laughter, kindness, and spirit touched everyone who knew her".
The family said that Harper's little sister "adored her big sister and is grieving an unimaginable loss".
"As a family, we are shattered, and words cannot capture the depth of our pain."
They added that the family hopes "her memory fuels action" to stop gun violence.
"No family should ever have to endure this kind of pain.... Change is possible, and it is necessary - so that Harper's story does not become yet another in a long line of tragedies."
‘We love you, you will always be with us’, says father of Minneapolis shooting victim
Officials have released few details so far about the suspect's background, but say she previously attended the church's school and had a mother who had worked there.
The 23-year-old suspect is believed to have approached the side of the Annunciation Church, which also houses a school, and fired dozens of shots through the windows using three firearms. Police also found a smoke bomb at the scene.
Witnesses have described seeing children bleeding as they fled from the church, begging for help from strangers.
In a news conference on Thursday, acting US Attorney General for Minnesota Joseph Thompson said "the shooter expressed hate towards many groups, including the Jewish community and towards President Trump".
The attacker, who died at the scene of a self-inflicted gunshot wound, left a note, officials said, but they added that a definitive motive may never be known.
"I won't dignify the attacker's words by repeating them, they are horrific and vile," said Mr Thompson.
Westman's name was legally changed from Robert to Robin in 2020, with the judge writing: "Minor child identifies as a female". However, some federal officials and police have referred to Westman as a man when discussing the attack.
Chief O'Hara told reporters that news outlets should stop using the killer's name, because "the purpose of the shooter's actions was to obtain notoriety."
He added that she, "like so many other mass shooters that we have seen in this country too often and around the world, had some deranged fascination with previous mass shootings".
US officials have warned for years that mass shooting can lead to copycat killings, as killers seek to become famous through their heinous crimes.
Several major news organisations have a policy of not identifying mass killers.
FBI Director Kash Patel has described the attack as "an act of domestic terrorism motivated by a hate-filled ideology".
In a post on X, Patel said that the attacker "left multiple anti-Catholic, anti-religious references" written on guns and in notes uncovered by investigators.
"Subject expressed hatred and violence toward Jewish people, writing Israel must fall,' 'Free Palestine,' and using explicit language related to the Holocaust," he wrote.
The killer also "wrote an explicit call for violence against President Trump on a firearm magazine".
In their news conference, officials confirmed that the attacker had previously attended the school. Her mother, Mary Grace Westman, previously worked at the school, and has so far not responded to law enforcement's attempts to contact her.
They also confirmed that three residences associated with the attacker, who was from suburban Minneapolis, have been searched by police.
