The masked man who is suspected of the abduction of Nancy Guthrie appears to have been at her front door earlier than Feb. 1, the night police believe she was kidnapped, sources familiar with the investigation told ABC News.

The image the FBI released of the suspect at her front door, without a backpack, was captured by her Nest doorbell camera on a day before the suspected abduction, the sources said.

The FBI said the images of the suspect with the backpack on are from “the morning of her disappearance,” Sunday, Feb. 1, when Guthrie failed to show up to watch a virtual church service.

One theory, according to the sources, is that the suspect approached the door the first time, noticed the camera and was scared off, only to return later, when he is seen tampering with the device and putting branches in front of the lens.

The FBI and the Pima County Sheriff’s Department declined to comment.

The gap could help explain why investigators have asked neighbors to check their home security systems for suspicious people and vehicles going back to Jan. 1, a month before the abduction.

The images are the most important pieces of evidence in the investigation into “Today” show host Savannah Guthrie’s mother’s disappearance, which has captured the attention of the nation for much of the last month.

So far, no suspect has been identified by officials in Nancy Guthrie’s disappearance.

Jason Pack, a former FBI agent, told ABC News that if it is the same person, “it could indicate that the person was there surveilling the place before the abduction happened.”

“The fact that there was preparation and planning, which makes it more of a sophisticated type of criminal activity than someone just showing up,” he said.