TIMELINE-Nancy Guthrie abduction case in Arizona

By Herbert Villarraga and Steve Gorman

TUCSON, Arizona, Feb 19 (Reuters) - The following is a chronology of key developments in what authorities describe as the abduction of Nancy Guthrie, the 84-year-old mother of NBC's "Today" show co-anchor Savannah Guthrie. She was last seen by family members on January 31 after spending the evening at the Tucson home of her older daughter, Annie Guthrie, and son-in-law.

February 1 - A doorbell video camera at the front door to Nancy Guthrie's Tucson house captures footage of a man wearing a ski mask, backpack, gloves and holstered gun tampering with the camera in the early morning. Guthrie's pacemaker app loses contact with her phone line about a half hour later. Shortly before noon, relatives notify authorities that Guthrie is missing after she failed to appear for Sunday church services.

February 4 - Savannah Guthrie, her sister Annie Guthrie, and brother Camron Guthrie post the first of several video messages about their mother's disappearance on social media, saying they are aware of ransom note reports in the media, and pleading for abductors to open communication with them.

February 5 - Authorities confirm that DNA tests showed that blood found on Guthrie's front porch came from her. The first of two deadlines set in a purported ransom letter passes at 5 p.m.

February 7 - Savannah Guthrie, flanked again by her sister and brother, releases a video statement pleading for her mother's return, saying, "This is very valuable to us and we will pay."

February 9 - Savannah Guthrie, in an Instagram video, says, "We believe our mom is still out there" and asks for the public's help in locating her. A second ransom deadline passes.

February 10 - The sheriff's department and FBI release the video footage of the armed man at Nancy Guthrie's door, a recording the sheriff later describes as the single biggest clue to surface in the case. Hours later, authorities search a home in the Arizona border town of Rio Rico, 60 miles (97 km) south of Tucson, and take a man into custody for questioning. He is released and no arrests are made. Savannah Guthrie re-posts the masked man's images on Instagram with the caption: "We believe she is still alive; bring her home."

February 15 - FBI says a DNA sample was obtained from a glove that was found near Nancy Guthrie's home and appears to match the pair worn by the masked man in the doorbell camera footage.

February 17 - The FBI says the glove DNA sample failed to produce a match in a search of known genetic profiles in a national database, dashing hopes for a major break in the case.