Savannah Guthrie's sister, Annie Guthrie, was the last person to see their mom, Nancy Guthrie, before she was reported missing in Arizona, Us Weekly can confirm. Pima County Sheriff Chris Nanos exclusively spoke to Us on Monday, February 2, revealing what police know about what happened in the hours leading up to her disappearance. "We have a start point," Nanos said. "The family took her home from dinner at about 9:30 to 9:45 [p.m.]" on Saturday, January 31. "So we would back that up to even say 9 or 8:30 p.m. to start looking." Nancy Guthrie, Savannah Guthrie, Annie Guthrie. Courtesy of Savannah Guthrie/Instagram Nanos confirmed that Annie, Savannah's older sister, was the last person to see Nancy, 84, prior to her reported disappearance. (Nancy shared daughters Annie and Savannah, 54, and son Camron Guthrie with late husband Charles Guthrie, who died after a heart attack at the age of 49.) The sheriff noted that Annie didn't raise any "red flags" about her mother's behavior during their last interaction. Police Call Savannah Guthrie's Mom Nancy's Home a 'Crime Scene' Amid Search According to Nanos, Nancy's family members "weren't alerted to her [missing] until about 11 in the morning," the following day, while police weren't called until 12:15 p.m. on Sunday, February 1. As a result, officials are investigating a timeline "anywhere from 9:30 p.m. to 11 [a.m.]" as the window of when Nancy went missing. "This is an 84-year-old lady who is safe in her own home asleep, and she is taken. That should never happen," Nanos told Us, noting that Savannah didn't "raise any concerns" about her mother's health prior to her disappearance. Savannah Guthrie, Nancy Guthrie, Annie Guthrie. Courtesy of Savannah Guthrie/Instagram News broke on Sunday that Nancy's whereabouts were unknown after officials received a 911 call that morning from a concerned family member. "This is very concerning to us. We don't typically get the sheriff out at a scene like this. But it's very concerning what we're learning from the house," sheriff Nanos said in a press conference on Sunday regarding the case. "And so we'll just continue. The detective's homicide team is out right now looking at the scene as well." He explained, "We've pretty much just thrown everything at this that we can," adding that Nancy "is not of good physical health, and so naturally that's a great concern." Nanos later added at the press conference that Nancy has "no cognitive issues at all." Neighbor of Savannah Guthrie's Mom Saw Her Day Before Disappearance "She's very alert, she's of good, sound mind," he shared, but pointed out that Nancy is "not in good" physical health. "I hope we find her safe and sound, but we can't ignore what's in front of us." Nanos confirmed that law enforcement was "not ruling out" foul play and had formally launched a criminal investigation into Nancy's disappearance. During a second press conference, authorities revealed that due to the crime scene - Nancy's home in Tucson, Arizona - they believe she "didn't leave on her own." The police added that they were looking at Nancy's case not as "a search mission as much" as a crime. Savannah Guthrie's Mom Appeared on 'Today' 2 Months Before She Went Missing On Monday, Savannah was noticeably absent from the Today show - she is currently in Arizona with her loved ones amid the search for her mother. In her absence, her fellow anchors shared a statement on her and her family's behalf. "We want to get right to what is a deeply personal story for us," coanchor Craig Melvin said during the broadcast. "Nancy Guthrie, Savannah's beloved mother, has been reported missing in Arizona." He and Sheinelle Jones then read Savannah's statement: "On behalf of our family, I want to thank everyone for the thoughts, prayers, and messages of support. Right now, our focus remains on the safe return of our dear mom. We thank law enforcement for their hard work on this case and encourage anyone with information to contact the Pima County Sheriff's Department." Nancy Guthrie, Savannah Guthrie. Courtesy of Savannah Guthrie/Instagram Jenna Bush Hager also discussed Savannah's mother's disappearance on Today With Jenna & Sheinelle on Monday. She revealed that Nancy "takes daily medication" that she needs "for survival," adding to the urgency in which they hope she is found. Sheriff Nanos told Us on Tuesday that after speaking with Nancy's medical team authorities "know the med she needs and going without her meds ... can be fatal. 24 hours later, time is of the essence here." Bush Hager, 44, meanwhile, told her viewers on Monday, "We are thinking of our dearest, dearest Savannah and her whole family right now. Our prayers obviously go out to Savannah." How 'Today' Anchor Savannah Guthrie's Family Found Out Mom Was Missing As the search continues, one of Nancy's neighbors spoke with Us about what has transpired in their community since police began investigating the case. "There were a lot of dark vans with blacked out wind