What we know about the search for Savannah Guthrie's mother Nancy

Nancy Guthrie, the 84-year-old mother of NBC News anchor Savannah Guthrie, vanished almost four weeks ago.

Investigators suspect she was abducted from her Tucson, Arizona, home in the middle of the night. She was reported missing on 1 February.

The Guthrie family has made repeated public pleas for her safe return, and has asked for proof that she is still alive, but a breakthrough has eluded the FBI and local police.

Investigators have been sifting through 40,000 leads.

Officials have released doorbell camera videos and images showing a masked and armed suspect on Guthrie's doorstep the night she disappeared.

The footage showed the suspect - who the FBI said appears to be a male between 5ft 9in and 5ft 10in (175-177cm) - covering a camera lens with some plants.

He was wearing a 25-litre Ozark Trail Hiker Pack backpack, the FBI added.

The man's clothes are believed to have been bought at Walmart, according to Nanos, the Pima County sheriff.

Nanos told the BBC's US partner CBS that investigators had been reviewing surveillance video from nearby Walmart outlets.

Investigators later said the suspect appeared to have visited Nancy Guthrie's front door earlier than the day she was taken, CBS reported, citing a law enforcement source.

An image released by authorities of a man without that backpack is from a separate, earlier visit to the property, but it is unclear how many days before the kidnapping it was taken.

The sheriff has also told CBS that investigators have not ruled out a theory that an accomplice was also involved in the suspected abduction.

Nanos has said that "all siblings and spouses" in the Guthrie family have been cleared as possible suspects in the case.

Investigators have found 16 gloves during their search - most of which are thought to have been discarded by people searching for Guthrie.

However, DNA evidence collected from one glove, found about two miles from Guthrie's home, was sent to a lab for testing.

"The one [glove] with the DNA profile recovered is different and appears to match the gloves of the subject in the surveillance video," the FBI said.

But officials later said the DNA produced no matches in Codis, the FBI's offender database. Sheriff Nanos told the BBC he still believed the DNA could play a role in the case.

"I just believe she's somewhere here locally," he added. "I don't know why."

Officials have found DNA at Guthrie's address that does not belong to her or anyone close to her.

They are also studying a series of apparent ransom notes that may have been sent by the abductor or abductors.

On 10 February, police detained a man in connection with the suspected abduction, before releasing him hours later.

Officers also searched a nearby home on 13 February and questioned a person during a traffic stop, but no arrests were made.

The department did not provide further details about the lead or the residents of the house, saying only that no-one was arrested.

US investigators have reportedly been in touch with Mexican authorities about the disappearance and Nancy Guthrie's family has contacted a Mexican non-profit that works to find missing people in the region.

The Guthrie family is offering a $1m reward to find Nancy.

That adds to an already $200,000 reward offered from the FBI and the Tucson Crime Stoppers.

President Donald Trump, who ordered federal authorities to help in the investigation, has called the case "very unusual".

Guthrie was last seen at her home in Catalina Foothills, an affluent neighbourhood roughly six miles (10km) north-east of Tucson, on 31 January evening, when family members dropped her off around 21:30 local time (04:30 GMT).

At 01:47 local time on 1 February, a doorbell camera to her home was disconnected and removed.

At 02:28, the app on Guthrie's pacemaker, an implanted cardiac device, disconnected from her phone.

Concern grew when members of her church noticed her absence at Sunday's service and notified her family.

After the family called 911, authorities began a search that soon included volunteers and federal officers from Border Patrol, which stretched into the next morning.

Officials warned that Guthrie 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.

Police also say they found blood on the floor of Guthrie's porch - which was confirmed to be hers.

A number of possible ransom notes have been reviewed by investigators, some of which were first sent to media outlets.

Authorities have not said that any of these has been verified as having been sent by Guthrie's suspected abductor.

At least one of them has been determined by the FBI to be fake, which led to the arrest of a man in California.

One of the possible notes was said by FBI Special Agent Heith Janke to have set a deadline for a multimillion-dollar sum to be paid in Bitcoin by 5 February, or a higher figure to be paid by 9 February.

On 6 February, authorities said they were investigating a new message. They did not say who received the note or provide any details about what it said.

In several emotional videos, Savannah Guthrie and her siblings have commented on the alleged ransom notes and pleaded for their mother's safe return.

On 4 February, Savannah said "we are ready to talk", telling the abductor or abductors directly that "we need to know without a doubt that she is alive and you have her".

In another video on 6 February, the family released a third video in which Savannah Guthrie said: "We received your message, and we understand. We beg you now to return our mother to us so that we can celebrate with her."

Further video updates have followed, including one that was shared on 12 February that showed images of a young Nancy with her children.

Twenty-four days after her mother went missing, Savannah offered the $1m reward, but acknowledged Nancy "may be lost".

Savannah Guthrie, 54, is an American broadcast journalist who has served as the co-anchor of NBC News' Today since 2012. She is also the network's chief legal correspondent and a primary anchor for its election coverage. Previously, she was NBC News' White House correspondent.

Guthrie was born in Australia, but when she was a toddler her family moved to Tucson, Arizona, where she spent most of her childhood. She did not travel back to Australia until 2015, visiting with Nancy.

"For my mum to come back and get to see where she used to live brings back a lot of happy memories with my dad," Savannah told the Daily Telegraph.

Guthrie, who maintains a public stance of political neutrality, has interviewed presidents Barack Obama, Joe Biden and Trump.

She has a law degree from Georgetown University and a bachelor's degree in journalism from the University of Arizona.

She has won an Edward R Murrow Award for ethical electronic journalism and multiple News Emmys, including for an interview with Trump a month before the 2020 election.