Elizabeth Thomas appears in a photo released by the Tennessee Bureau of Investigation, March 2017. Getty Images

Investigators confirmed Friday the first confirmed sighting of missing Tennessee teenager Elizabeth Thomas and former teacher Tad Cummins since they vanished more than two weeks ago. The Tennesee Bureau of Investigation said it obtained surveillance footage from an Oklahoma City Walmart that showed the two shopping on March 15.

"Cummins used cash to purchase various food items, but did not purchase anything else of significance," the TBI wrote in a news release. "The surveillance images of Cummins and Thomas – the first obtained by investigators since the alleged kidnapping on March 13th – clearly show Tad Cummins with an altered appearance to darken his hair. The same images show Elizabeth may currently have red hair. Efforts to determine what vehicle they were traveling in remain ongoing."

Cummins, 50, has been accused of kidnapping former student Thomas, 15, in the wake of a school investigation into their relationship. He was thought to be armed.

As police continue to search for the duo, here's a full timeline of recent events in their case, with information from the Tennesseean, ABC News and CNN.

Jan. 23: A student at Culleoka Unit School sees Thomas and Cummins kissing at school. "It wasn't like a make-out kiss, just a peck on the lips," the student said in a statement.

Jan. 24: The student asks Cummins about the relationship. He tells her he was a father figure and best friend to Thomas. The student goes to administrators about the kiss.

Jan. 25: The school district begins an investigation, interviewing the witnesses, Thomas, Cummins and their peers.

Jan. 27: Culleoka takes Thomas out of Cummins' class. Cummins and Thomas also go on a field trip together, according to the Thomas family attorney.

Jan. 31: Police tell the school district Cummins is under criminal investigation. The district sends its paperwork on the duo to law enforcement. Cummins is told not to let Thomas into his classroom.

Feb. 1: Thomas' father learns of the kissing claims. He calls the school and demands to know what's going on.

Feb. 3: Thomas spends a half hour in Cummins' classroom. Cummins is reprimanded.

Feb. 6: Cummins is suspended from the school district without pay. The Thomas family attorney says the girl's phone history shows she's continued to contact the teacher.

March 5: Cummins does an internet search for "teen marriage," according to the TBI.

March 7: Cummins is seen in a Walmart buying hair dye, though the TBI later finds it "was not connected to any plan to change his appearance or that of Elizabeth Thomas."

March 10: Cummins tries to find out how his car may be tracked by police.

March 13: Elizabeth tells a family member she'll be home by 6 p.m. that night and if she's not they should call the police, according to another sibling. She gets dropped off at a restaurant in Columbia at about 8 a.m. Cummins is seen getting gas at the same time in the same area.

Thomas is listed as missing at about 1 p.m. local time. By 3 p.m. local time, Thomas is thought to be in Decatur, Alabama.

March 14: Cummins is fired and charged with sexual contact with a minor. An amber alert goes out for Thomas.

March 16: TBI spokesperson Josh Devine tells reporters the duo could "frankly, be anywhere at this point."

March 17: Cummins' wife, Jill Cummins, gives a news conference. "I had no idea my husband was involved with anything that has led to all this," she says. "My heart breaks for the family of Beth Thomas. Tad, this is not you ... Please do the right thing and turn yourself into the police and bring Beth home."

March 23: Investigators check "in on a possible lead" in Texas, according to DeVine.

March 24: The school district announces plans to create a task force to update its policies for telling parents about "any range of potential student and/or faculty/staff incidents."

March 29: The TBI translates its amber alert notice into Spanish as authorities tell reporters the couple could be in Mexico.

March 30: Investigators reject rumors that Thomas and Cummins have been seen in Memphis, Tennessee.

March 31: Law enforcement officials announce the first confirmed sighting of Thomas and Cummins — on March 15, in an Oklahoma City Walmart. Both have different hair colors than they previously did.