Chelsea Cook locked herself in the bathroom while she was on the phone with a 911 operator, the court document said. When she eventually left the bathroom, she walked toward her coat.
“(Cook) then suddenly pulled out a handgun and fired three to five rounds at the victim,” the affidavit said. “The victim fell back and landed on the couch.”
Travis Cook managed to get the gun away from his ex-wife and, as he tried to help a dying Williams, Chelsea Cook sat down in a recliner with her children, the affidavit said. When she again tried to get her coat and leave, Travis Cook pinned her against a wall until police officers arrived.
“The witness alerted officers that he had a handgun in his waistband and informed officers that (Chelsea Cook) had just shot his girlfriend/victim,” the affidavit said. “Officers found the victim with a least two gunshots to the torso. The victim was transported to a local hospital, where she eventually succumbed to her injuries.”
The victim's family told the Associated Press that Chelsea Cook subjected Williams to harassment, both online and in person, for months before the shooting. Williams had been dating Travis Cook, a coworker at the bank where she worked as a teller, for six months when she was killed.
"I worried for her safety every day," Williams' mother, Tawny Williams, told the AP.
Despite the alleged harassment, Lisa Williams was eager to celebrate the Christmas season with her boyfriend and his children. Her sister, Bekah Williams, said she’d left her own family’s Thanksgiving gathering in Centennial Park, Arizona, early to make the drive back to Utah.
"I spoke to her an hour or so before it all happened and she was so excited to give those kids something happy," Bekah Williams said.
The grieving sister told the AP that Lisa Williams was reluctant to report the harassment to police out of fear that it would make the situation harder for the Cook twins. She told the news agency that it would have been better for all involved if her sister had called and reported each incident.
Bekah Williams said she called Chelsea Cook’s school herself and reported her behavior to administrators there.
The AP reported that school officials were apparently not aware that Chelsea Cook had been arrested Oct. 16 on a charge of committing domestic violence in front of children. Cook was required to report the arrest to her superintendent within 48 hours but failed to do so.
Details of that arrest were not available, but Bekah Williams told the AP it did not involve her sister.
The state of Utah also flags teacher arrests through fingerprints, but the notification in the misdemeanor domestic violence case did not come until after Lisa Williams was slain, the AP reported.
Tawny Williams wrote on Facebook that her daughter was killed while she and the children decorated a Christmas tree with homemade ornaments they'd made together.
"She was so kind, sweet, generous, loving, and brought joy and excitement to every aspect of life," Tawny Williams wrote. "Please share the beauty of her life rather than the monster that ripped her from ours. I am asking that anyone that has posted the picture and article with the evil killer as the subject please remove it and share Lisa's beauty instead.
“She was magic, and I want her remembered for how she lived and not for how she was killed.”
Lisa Williams' obituary described her as a shy, quiet woman who moved from Arizona, where she was raised, to her native Utah in late 2015 to help care for a critically ill sister. She got a job at the bank, one that challenged her quiet nature.
"She found pride in her newfound ability to engage in 'small talk,'" her obituary read.
She loved children, particularly her nieces and nephews, her family wrote.
Bekah Williams described her younger sister on a GoFundMe memorial page as "the most amazing and sincere individual."
"Everywhere Lisa went, she spread beauty and happiness," she wrote. "She loved all of the small things and was enamored with making every little thing special and beautiful. From our Parisian-themed dates to finding the saddest plant in the store as a project to bring back to life, she made everything better."
She wrote that her sister loved bigger than anyone she knew.
"Our beautiful little sister, daughter and friend, you are so very loved and missed immensely," Bekah Williams wrote.
Skyridge High School is part of the Alpine School District, which covers northern Utah County. The school's principal, Joel Perkins, sent an email to parents the day after the shooting to let them know that Chelsea Cook had been arrested.
The school district provided counselors for students trying to comprehend the murder charge against one of their more popular teachers, KUTV in Salt Lake City reported. Cook has been fired and a substitute teacher will take over her class for the remainder of the school year, the news station said.
"I never could have seen this happening," senior Kaleb Latimer, who acted as Cook's teaching assistant, told KUTV. "I was in her class almost every day for two years. She was my favorite teacher. She was one of the classes I would look forward to going to."
Latimer said he noticed a change in his teacher following her divorce, which the AP reported was finalized in January.
"Before her divorce, you could tell she was super happy all the time and, when she got divorced, she missed a couple days of class, which she never really did," Latimer told KUTV. "After that, it was just kind of different, I guess."
Mike Jensen, whose daughter was in Cook’s health class this year, told the news station he was shocked to hear of the teacher’s arrest.
"I want to know what drove her to do it," Jensen said. "I just hope that she does OK wherever she ends up."