(NEXSTAR) – Blood found outside the front door of Nancy Guthrie's home has been linked back to the 84-year-old, Pima County Sheriff Chris Nanos confirmed on Thursday. Nanos said investigators believe Guthrie is "still out there," despite authorities not knowing whether she's receiving the medication she has been prescribed. Guthrie was last seen Saturday night when her son-in-law, Tommaso Cioni, dropped her off at her Tucson, Arizona, home. Nanos told The New York Times that Guthrie had been at dinner with Cioni and her daughter, Annie, who lives nearby. Her family reported her missing on Sunday when a church member informed them that Guthrie had missed church. Authorities have been searching for Guthrie ever since, warning that she has “some physical ailments, has some physical challenges, [and] is in need of medication.” Five days in, Nanos said no suspect has been identified. The FBI is now offering a $50,000 reward for information leading to Guthrie, or the arrest and conviction of anyone involved in her disappearance. The non-profit 88-CRIME previously offered a reward of up to $2,500 for information leading to an arrest, while Victory Church in Albany, New York, has offered a $25,000 reward for information that leads to finding Guthrie, The Associated Press reported on Wednesday. The FBI also acknowledged the alleged ransom notes that multiple media outlets received earlier this week. Heith Janke, the special agent in charge of the FBI’s Phoenix Office, said Thursday that a person behind an alleged imposter ransom note had been arrested but additional details were not immediately available.