Late Wednesday night, the tip they were desperately hoping for finally arrived.
It came from a caller who told investigators that the 50-year-old Cummins and the teenager he is accused of abducting might be living in a remote cabin near Cecilville, California, a onetime mining town about 100 miles from the Oregon border.
Speaking to reporters at a news conference Thursday afternoon, TBI spokesman Josh DeVine said investigators quickly coordinated with the Siskiyou County Sheriff's Office, which was able to locate a silver Nissan Rogue belonging to Cummins and keep the vehicle under surveillance for several hours.
"The area where the pair was reported to be is a very remote, isolated area with no or limited cellphone services," DeVine said. "As daylight broke this morning, they were able to take Tad Cummins into custody and safely recover Elizabeth without incident."
Authorities said Elizabeth was physically unharmed, but they declined to comment on her emotional well-being or where the pair has been since they vanished last month.
TBI Director Mark Gwyn said Elizabeth will be flown back to Tennessee in a TBI aircraft to be reunited with her family. At the same time, he noted, investigators from TBI, the FBI and the Maury County Sheriff's Office are on their way to Northern California to continue their investigation.
Gwyn said Cummins - who is being held by the Siskiyou County Sheriff's Department without bond - faces charges that "could keep him behind bars for many years."
"What happened in California this morning, however, proves it only takes one person to lead to a successful end," he added. "We are extremely thankful the hard work of all partners in this search has paid off. We're also grateful for the public's support and vigilance throughout this search effort."
Once Cummins is extradited to Tennessee, he will be charged with sexual contact with a minor and aggravated kidnapping, authorities said.
Acting U.S. attorney Jack Smith said his office had also filed a federal charge of transportation of a minor across state lines for criminal sexual intercourse - a charge that carries a minimum 10 year sentence.
Anthony Thomas, Elizabeth's father, told NBC affiliate WSMV-TV that he wasn't surprised that they were in the northwest and said he'd heard the pair were in a commune.
"I'm very happy," he said. "She's probably going to be hungry."
Maury County Public Schools also issued statement Thursday, calling Elizabeth's return "wonderful news for our community."
"Thanks go to all who have kept the message of finding Elizabeth Thomas and working on her safe return as top-of-mind throughout the nation," it said.
The teen and Cummins - a 50-year-old from Middle Tennessee - had been missing since March 13, when an Amber Alert was issued. Cummins was Elizabeth's high school teacher at Culleoka Unit School.
"Investigative efforts have revealed a troubling pattern of behavior by Tad Cummins, suggesting the 50-year-old may have been abusing his role as a teacher to groom this vulnerable young girl for some time in an effort to lure and potentially sexually exploit her," the agency said in a statewide Amber Alert.
"Having now been on the run for more than five days, Cummins may have taken her, frankly, anywhere," the agency said last month.
On March 13, video surveillance at a Columbia gas station showed Cummins filling up his silver Nissan Rogue. A short time later, investigators say, he drove to a Shoney's restaurant, where Elizabeth had been dropped off by a friend and was waiting. Investigators said they think he manipulated her into leaving with him, but he wasn't authorized to take a minor, and she wasn't old enough to consent. That afternoon, investigators say, they determined Elizabeth was 80 miles away in Decatur, Alabama.
Then, nothing. After their disappearance, investigators said they had received hundreds of tips from 24 states, but not enough information to tighten the dragnet despite a multi-state manhunt and Cummins' addition to Tennessee's most-wanted list.
In a news release, the TBI said Cummins might be keeping Elizabeth out of sight of authorities, possibly sleeping in his car or in a rural community.
Last month, the agency released new images of Cummins in an effort to keep the case in the spotlight. The pictures were from a week before Cummins and Elizabeth disappeared, and they showed him wearing a camouflage cap and pushing a shopping cart at a store.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)