Frustration is mounting in the investigation into Nancy Guthrie's disappearance as cops admit they have found no suspects over six days into the search.

In the days since the 84-year-old vanished from her home in Tucson, Arizona overnight Saturday, investigators have returned to the scene three times to seize evidence.

The latest search on Friday came after a 'new message' was sent to KOLD, a local Tucson news outlet, that appeared to be sent by people claiming to be holding Nancy for ransom.

Messages were also sent to KOLD and TMZ earlier in the week, which officials say they have not verified as legitimate but are taking 'seriously' as leads.

On Thursday, Nancy's Today Show host daughter Savannah joined siblings Annie and Camron to share a video pleading with their mother's abductors to communicate with them, if the ransom notes turn out to be real.

The man leading the search, Pima County Sheriff Chris Nanos, said at a press conference hours earlier that he believes Nancy is still alive.

However, Nanos has come under scrutiny amid the ongoing investigation - including sources within his department telling the Daily Mail that he made a series of missteps that slowed the search in its crucial first hours.

With investigators under the spotlight, here the Daily Mail takes a look at the key evidence in the case.

Nancy Guthrie, 84, the mother of Today Show star Savannah Guthrie, vanished from her home in Tucson, Arizona on the night of January 31

Over six days into the search, investigators have failed to arrest any suspects, mounting pressure on the ongoing search. Police are seen arriving at Nancy's home for a third evidence search on Friday evening

Your browser does not support iframes.

Blood found on Nancy's doorstep

Soon after Nancy's disappearance shocked the nation, officials said they found critical evidence that suggested 'forced entry' at the scene.

The crime scene at Nancy's home was released by investigators within two days, and soon after images emerged showing blood spatter around her front door.

The images showed blood appeared to have fallen in droplets from her door to her driveway.

Forensics testing found the blood belonged to Nancy, and the droplet pattern indicated she may have walked from her door while bleeding.

Blood was spotted on the walkway of Nancy's Tucson, Arizona home

The images showed blood appeared to have fallen in droplets from her door to her driveway. Forensics testing found the blood belonged to Nancy, and the droplet pattern indicated she may have walked from her door while bleeding

Missing doorbell camera

Among the early indications that foul play may have played a role in the incident was a doorbell camera fitted to Nancy Guthrie's front door appeared to have been removed.

At a press conference on Thursday, Sheriff Nanos revealed that investigators found the doorbell camera disconnected at 1:47am in the early hours of February 1 - around the time Nancy was believed to have been abducted.

Nanos said at 2:12am, a person was detected by the camera's sensors, but no images were taken by the device because it had been disconnected.

On Friday, Nanos said that investigators were unable to access any data from the entire evening on the device, because Nancy did not have an active subscription.

The sheriff said he was 'disappointed' that the doorbell camera failed to provide new evidence - marking a significant setback in the ongoing search.

A doorbell camera fitted to Nancy's front door was disconnected at 1:47am on the night she vanished

Officials say Nancy, 84, is frail and has poor mobility, and suffers from a condition that requires her to take medication daily

Officials previously said they have no reason to believe Nancy may have been targeted because of her daughter, but have also not ruled out any inquiries. Savannah Guthrie earns a reported $8 million salary at NBC, and has a net worth estimated at around $40 million

Podcast All episodes

Nancy's pacemaker disconnected

At the press conference on Thursday, Nanos also revealed that Nancy's pacemaker app - a device that synced data from her heartbeat - cut off from her Apple Watch's Bluetooth at 2:28am on Sunday.

Nancy's Apple Watch was found inside the home on Sunday morning, and the device would likely have disconnected when it was taken out of range, indicating she was taken from the home in the dead of night.

'White van' spotted in the neighborhood

One of Nancy's neighbors also revealed this week that a suspicious white van was looming on their street before her abduction.

Brett McIntire, 72, reported the vehicle to police after noticing it lacked any company branding, unlike normal work vehicles, he told the New York Post.

'It was a white van, full-sized, with no printing on the sides. It was parked on the street,' he said.

He spotted the vehicle a few days before Nancy's disappearance and said that he answered some basic questions from police about the sighting.

All the evidence in the Nancy Guthrie case amid ongoing search