Ex-teacher accused of kidnapping teen believed to have watched TV show about living off the grid: Sources Tad Cummins, 50, is accused of kidnapping Elizabeth Thomas, 15, on March 13.

 -- A former Tennessee teacher accused of kidnapping his 15-year-old student is believed to have watched a TV show about living off the grid before the pair disappeared, law enforcement sources told ABC News.

Tad Cummins, 50, is accused of kidnapping Elizabeth Thomas on March 13. As the manhunt intensifies, officials say there have been no credible sightings of the duo. Tennessee Bureau of Investigation spokesman Josh DeVine told ABC News that if the duo isn’t outside the Southeast, they are likely "off the grid" in a rural area.

Three days before the alleged kidnapping, Cummins did online research about his car "to determine if certain features could be tracked by law enforcement," the TBI said Tuesday.

Cummins also researched if his SUV was suitable for camping, law enforcement officials said.

Cummins, a married father and grandfather, researched teen marriage online as well, specifically the age of consent, according to law enforcement officials.

The TBI said that Cummins, who was fired one day after the alleged kidnapping, "may have been abusing his role as a teacher to groom [the teen] ... in an effort to lure and potentially sexually exploit her."

One of Thomas's schoolmates had reported seeing Thomas and Cummins kiss in his classroom on Jan. 23, according to a school district investigative report, but Thomas and Cummins denied the claim.

Thomas' sister told ABC News that the 15-year-old was bullied in school by students and teachers after the reported kiss and told her "I just have to get away, we have to get away."

"I can't handle this anymore . .. all the teachers, all the kids constantly saying mean things, I can't handle it,’" the sister said.

Cummins is wanted on allegations of aggravated kidnapping and sexual contact with a minor. An Amber Alert has been issued for Thomas.

Authorities say Cummins is believed to be armed and that the teen is "in imminent danger."

Authorities said neither Thomas nor Cummins has been in touch with family members.

Cummins' wife, Jill, pleaded with her husband Friday to "come home." "I had no idea my husband was involved with anything that has led to all this. My heart breaks for the family of Beth Thomas,” she said. “Tad, this is not you. This is not who you are. We can help you get through this. ... Your family wants their poppy back. Please do the right thing and turn yourself into the police and bring Beth home.”

In an interview with ABC News Monday, the teen's father, Anthony Thomas, said he wants his daughter to "please let us know you are all right and please come home to us."

Thomas family attorney Jason Whatley told ABC News that Cummins was "taking advantage” of his student and "manipulating her into leaving with him."

"We are very concerned about the control that he has over her," Whatley said. "We believe that is 100 percent the reason why she is missing at this point. He is the problem, she is not. She’s a child, she’s a victim."

Cummins is described as 6 feet tall and weighs about 200 pounds. He may be driving a 2015 silver Nissan Rogue with a Tennessee license plate number 976-ZPT.

Elizabeth Thomas is described as 5-foot-5 and weighs 120 pounds. She was last seen wearing leggings and a flannel shirt.

Authorities are asking that anyone with information call 1-800-TBI-FIND and that anyone who sees a car with a Tennessee license plate 976-ZPT call 911. A $1,000 reward is available for information leading to Cummins' arrest.

ABC News' Eva Pilgrim and Janice McDonald contributed to this report.