Mourning the loss of a mass-shooting victim and the gunman himself -- their daughter and their son -- the Betts family is "shocked and devastated by the events of Sunday morning" in Dayton, Ohio, they said in a statement.
The family also offered "their most heartfelt prayers and condolences to all of the victims, their families and friends," according to a statement read Tuesday by Police Chief Doug Doherty of nearby Bellbrook, Ohio.
Connor Betts, 24, who armed himself with a .223-caliber high-capacity rifle, fired 41 shots early Sunday, killing his sister, Megan Betts, 22, and eight others in a popular nightlife district, police said. Twenty-seven people were injured in the attack before patrol officers killed Connor Betts just 30 seconds after he opened fire.
The Betts family will cooperate with law enforcement in the "investigation into this tragedy," according to the statement. They also asked for privacy to mourn their loss and "to process the horror of Sunday's events."
He once kept a 'hit list,' classmates say
What motivated Betts to kill remains unknown. He had an obsession with violence and had expressed a desire to commit a mass shooting, Dayton Police Chief Richard Biehl said Tuesday.
A Twitter account that appears to belong to Betts expressed support for Antifa, or anti-fascist, protesters, and also retweeted extreme left-wing and anti-police posts.
Meanwhile, former high school classmates recalled how Betts kept a "hit list" of people he wanted to kill or rape. He also fronted a "pornogrind" band and sang songs with graphic, violent lyrics, a music booker said. Authorities searching his family home found writings that expressed an interest in killing people, two law enforcement sources told CNN.
"(He was) very specifically seeking out information that promotes violence," FBI Special Agent in Charge Todd Wickerham said Tuesday at a news conference.
Megan Betts 'was good to her roots'
Friends of Megan Betts have described her as kind and generous.
"From the start, I knew Megan had a good heart," her friend, Sarah Coffee, told CNN. "She was good to her roots, and I don't think she could have watched someone suffer and not done anything."
Artistic in nature, Megan was known for drawing, playing the trumpet and acting in her high school's drama program. Friends told CNN that Megan was always laughing and they wish that she be remembered as a beloved friend: "She was someone who made the world better, happier," Coffee said.
The Betts family, in its statement, thanked first responders, who all "provided aid and comfort to the victims," as well as the Bellbrook Police Department for "providing a peaceful environment surrounding their home."