According to investigators, the FBI analyzed footage captured by a doorbell camera outside the residence. Based on that video, officials believe the suspect is a male standing between 5 feet 9 inches (175 cm) and 5 feet 10 inches tall, with an average build, News.Az reports, citing BBC.
This marks the first time the individual seen in the surveillance footage has been formally identified as a suspect in the case. The disappearance has attracted significant public attention, both across the United States and internationally, as the investigation continues.
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Nancy Guthrie, 84, vanished in the middle of the night from her home in Tucson and was last seen two weeks ago. Authorities have stated that they believe she was taken against her will.
In its latest statement, the FBI said it had been able to establish identifying details after carrying out a forensic analysis.
It highlighted the backpack being worn by the suspect in the video, which was released earlier this week, and identified it is a 25-litre Ozark Trail Hiker Pack.
A pair of black gloves has also been found during the search for Guthrie, the BBC's US broadcast partner CBS reported on Thursday.
Nancy Guthrie was last seen on the evening of Saturday 31 January when family members dropped her home. Members of her church noticed her absence at Sunday's service and notified her family.
Officials have warned she may be in dire health without her medication. Pima County Sheriff Chris Nanos said she was "not in good physical health" but had no reported cognitive issues.
Since 1 February, the FBI said it had received more than 13,000 tips in relation to the case - including 4,000 in the 24 hours after the doorbell camera footage was released.
It is offering money to anyone who comes forward with information about her disappearance and has now doubled the reward from $50,000 (£36,700) to $100,000.
Earlier this week, a man was detained in connection with Guthrie's disappearance and his home in Rio Rico - south of Tucson, Arizona - was searched before he was released.
Speaking to reporters following the incident and said he did not know who Nancy Guthrie was.
Savannah Guthrie and her two siblings have released a number of social media pleas directed at their mother's potential abductors.
They believe she is still alive and have indicated they would be willing to pay for her return.
