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.

Nancy Guthrie 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 Pima County Sheriff's Department and FBI release doorbell video footage of the armed man at Nancy Guthrie's home, which the sheriff later describes as the single biggest clue to emerge 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 reposts images of the masked man on Instagram with the caption: "We believe she is still alive; bring her home."

February 15 - A DNA sample is obtained from gloves that were found discarded about 2 miles from Nancy Guthrie's home and resemble the pair worn by the masked man in the doorbell camera footage, authorities say.

February 17 - The glove DNA sample fails to produce a match in a search of known genetic profiles in a national database known as CODIS, according to the FBI and sheriff.

February 24 - The family offers a reward of up to $1 million for information that leads to the recovery of Nancy Guthrie in a video posted on Instagram by Savannah Guthrie, which for the first time addresses the possibility that Nancy Guthrie is dead.

March 4 - The same gloves are traced through further DNA analysis to a local restaurant employee who is not considered a suspect in the case, the sheriff's department says, indicating a dead end for what had been a once-promising lead.

April 6 - Savannah Guthrie returns to her job in the co-anchor's chair of NBC's "Today" show.

-Compiled by Steve Gorman in Los Angeles; Editing by Donna Bryson, Rod Nickel, Ros Russell/Reuters