What we know about former Tenn. teacher Tad Cummins' relationship with 15-year-old student Elizabeth Thomas

— -- After more than a month on the run amid a nationwide manhunt, former Tennessee teacher Tad Cummins was found with his 15-year-old student, Elizabeth Thomas, in far northern California.

Cummins was arrested and charged with aggravated kidnapping and sexual contact with a minor. Today, the FBI took custody of Cummins under a federal warrant, which supersedes all local charges. The FBI is expected to take him back to Tennessee.

Elizabeth will be reunited with her family in Tennessee today.

Here's what is known about the days leading up to her alleged abduction, her time spent on the run with Cummins and how authorities finally located them thousands of miles away.

Jan. 23

One of Elizabeth's schoolmates reported seeing her and Cummins kiss in his classroom at Culleoka Unit School in Culleoka, Tennessee, on Jan. 23. Both denied the claim, but the school district in Maury County decided to investigate the allegation.

Jan. 30

A report from the school district dated Jan. 30 stated that neither Cummins nor Elizabeth "admitted to behaving inappropriately towards the other."Cummins said Elizabeth, a student in his forensics class, is "a really good friend" who sees him "when she needs someone to calm her down." He said he loved his wife and would never cheat on her, the report stated.

The report concluded that it "could not be confirmed" the alleged kiss happened. However, the report said Elizabeth would be removed from Cummins' class and that "Cummins will be reprimanded in regards to his duty to uphold his professional responsibility and behavior."

Feb. 3

The school district wrote a letter to Cummins on Feb. 3, stating that Elizabeth was in the teacher’s classroom that day, which the letter said violated a previous order by the school district.

Feb. 6

The school district wrote another letter to Cummins on Feb. 6, telling him he is suspended without pay immediately "pending an investigation."

An attorney for the Thomas family wrote a letter to the school district superintendent on Feb. 6, claiming that Elizabeth’s father was never alerted by the district about the alleged incident and found out about it on Jan. 31, more than a week after the kiss allegedly happened, when sheriff's deputies called to ask him questions.

The lawyer's letter also suggested the teen was communicating with the teacher through her cellphone. "Upon inspection of her cellphone the two are also having telephone communications," the attorney's letter stated.

March 5

Cummins, a married father and grandfather, researched "teen marriage" online, specifically the age of consent, on March 5, according to the Tennessee Bureau of Investigation.

March 10

Cummins conducted an online search about his car "to determine if certain features could be tracked by law enforcement," according to the Tennessee Bureau of Investigation.

March 13

Elizabeth urgently woke up her sister Sarah on March 13 and made her promise to call the police if she’s not home by 6 p.m. that night.

Sarah later told ABC News that Elizabeth sounded "serious," not happy.

"She's not a serious person," Sarah said.

Elizabeth was seen around 7:30 a.m. or 8 a.m. local time at a Shoney's restaurant in Columbia, Tennessee, where she is dropped off by a friend, according to the Tennessee Bureau of Investigation. She never returned home that night.

Surveillance footage from a gas station near the restaurant appeared to show Cummins at about 8:30 a.m. filling up his silver Nissan Rogue.

Later that same afternoon, a cellphone ping placed the pair in Decatur, Alabama, according to the Tennessee Bureau of Investigation.

March 14

Cummins was officially fired from his teaching job at Culleoka Unit School.

An Amber Alert was issued for Elizabeth.

March 15

Surveillance cameras at a Walmart in Oklahoma City, Oklahoma, captured Cummins and Elizabeth in the store on the afternoon of March 15.

Investigators later obtained and released images from the surveillance footage.

The footage showed the pair entering the Walmart together, where Cummins used cash to buy food. He didn’t buy "anything else of significance," according to the Tennessee Bureau of Investigation.

In the video, Cummins has "an altered appearance to darken his hair" and indicated that "Elizabeth may currently have red hair," according to the Tennessee Bureau of Investigation.

March 17

Cummins, wanted on allegations of aggravated kidnapping and sexual contact with a minor, was added to Tennessee’s 10 most wanted list.

March 28

Brent Cooper, the district attorney general for Giles, Lawrence, Maury and Wayne counties in Tennessee, asked members of the public to share the Amber Alert for Elizabeth with friends and family members in Mexico and Central America, adding that Mexican law enforcement had been notified and "it's possible that's where they are."

Cooper said Cummins "planned this in such a way that he had a 24-hour head start ... easily enough time for him to make it to Mexico."

March 31

A lawyer for Cummins' wife, Jill Cummins, said she had filed for divorce after 31 years of marriage.

"Jill will attempt to move forward with her life," attorney Michael Cox said in a statement provided to ABC News. "Jill continues to pray for the safe return of Elizabeth Thomas and for a peaceful resolution to this ordeal."

April 11

Cooper told ABC News that Cummins is on medication to control his blood pressure and should need a refill. Pharmacists were asked to be on alert for customers who look like Cummins or Elizabeth.

Cooper also told ABC News that Cummins left a note for his wife the morning he vanished. Cooper didn’t provide details on what was in the note, but said it appeared to have been a diversion to throw investigators off the trail.

April 18

Griffin Barry, a resident in far northern California, met Cummins and Elizabeth at a gas station in a very rural area of Cecilville.

Cummins told Barry, who lives on a property that includes the gas station, their names are John and Joanna and that they need money for gas, food and a place to stay.

Barry paid to fuel up their car, gave them an extra $40 in cash and set them up in a nearby cabin on the same property where he resides.

Barry didn't talk much with the pair, he said, but became increasingly suspicious the more he interacts with them.

"The girl wasn't really looking at me or anything and he was always dominating the conversation. That kind of clues people in," Barry later told ABC News' "Good Morning America."

April 19

After realizing who Cummins and Elizabeth really were, Barry called 911 on April 19.

"I had a photo of him that was the Amber Alert and I was like, that’s definitely the guy, and then we saw the car as well and it matched up. Then we called the police right after that," Barry later told "GMA."

Around 11 p.m. local time on April 19, the Tennessee Bureau of Investigation received a call to its tip line about a possible sighting of the duo, according to the bureau’s public information officer, Josh Devine.

The Siskiyou County Sheriff's Department in northern California, received a similar tip, according to Devine.

Investigators located a Nissan Rogue and were able to confirm through its VIN number that it belonged to Cummins. The car was kept under surveillance for several hours.

April 20

Authorities from the Siskiyou County Sheriff's Department located Cummins and Elizabeth at a cabin in a rural area in remote Cecilville, nearly 2,500 miles from Elizabeth’s home in Tennessee.

Authorities were deployed to the location around 2 a.m. local time and deputies set up a perimeter around the cabin. They elected to wait until daylight to arrest Cummins as he exited the residence, according to the sheriff’s department.

Around 9:30 a.m. local time, Cummins exited the cabin and surrendered without incident. He was subsequently placed under arrest. Two loaded handguns were found in the cabin, according to the sheriff's department.

Elizabeth also exited the cabin and was safely recovered by law enforcement officers.

"After we placed them into protective custody, she was laughing, she was crying. She was kind of an emotional roller coaster, as you can imagine," Lieutenant Behr Tharsing of the Siskiyou County Sheriff’s Department later told "GMA."

Cummins was charged with aggravated kidnapping and sexual contact with a minor, according to Cooper.

The U.S. State Attorney's Office for the Middle District of Tennessee also filed a federal charge of transportation of a minor across state lines with intent of having criminal sexual intercourse against Cummins, according to U.S. attorney Jack Smith. The charge carries a mandatory minimum sentence of 10 years in prison.

Cummins also faces charges in California’s Siskiyou County for kidnapping and possession of stolen property, according to the sheriff's department. The charges are pending review by Siskiyou County District Attorney Kirk Andrus.

Cummins was in the custody of the Siskiyou County Sheriff’s Department without bond, until today.

April 21

FBI officials arrived at the Siskiyou County Sheriff’s Department around 8:30 a.m. local time on April 21 with a federal warrant to take custody of Cummins, superseding all local charges in Tennessee and possible charges in California.

Cummins was in the custody of the FBI and was expected to be taken back to Tennessee.

ABC News' Elisabeth Bognar, William Gretsky, Michael Edison Hayden, Katie Kindelan, Dee Morales, Lauren Putrino, Glenn Ruppel, Emily Shapiro, Jason Volack, Kayna Whitworth, Nery Ynclan and Robert Zepeda contributed to this report.