Story highlights Former sister-in-law describes the suspect as aggressive, "weird and unusual"

A FBI special agent says he is hopeful the two missing girls are alive

Jo Ann Bain and her oldest daughter were found dead in Mississippi last week

Police are searching for suspect Adam Mayes and the other two girls

Police in Tennessee have arrested the ex-wife and mother of Adam Mayes, the man suspected of kidnapping Jo Ann Bain and her three daughters, state authorities said Tuesday.

The mother, 65-year-old Mary Frances Mayes, and the ex-wife, Teresa Ann Mayes, 30, were arrested Monday, according to the Tennessee Bureau of Investigation (TBI). Teresa Mayes has been charged with four counts of especially aggravated kidnapping, while Mary Frances Mayes has been charged with four counts of conspiracy to commit especially aggravated kidnapping.

They appeared before a judge Tuesday morning and were being held in the Hardeman County Jail, Deputy court clerk Pat Kirk said.

According to an arrest warrant, Teresa Mayes admitted driving a vehicle containing Jo Ann Bain and her three daughters from Hardeman County to Union County, Mississippi. Bain and her oldest daughter, Adrienne, suffered "serious bodily injury as a result of their removal or confinement," according to the warrant.

Convictions carry possible sentences of 15 to 60 years in prison under Tennessee law. Bond has been set at $500,000 for Teresa Mayes, while Mary Frances Mayes' bond was set at $300,000, Deputy Clerk Rhonda Sipes said. Both women were assigned court-appointed attorneys and are slated to make their next appearance in court on May 22.

Mary Frances Mayes

Teresa Ann Mayes

The bodies of Jo Ann Bain and her eldest daughter, Adrienne, were found Saturday at a home in Guntown, Mississippi, that has been linked to Adam Mayes, the TBI said. Investigators are are still searching for Adam Mayes and Bain's two younger daughters, Alexandria Bain, 12, and Kyliyah Bain, 8.

"We are absolutely hopeful. Currently that's what we believe, and we do believe that they are still with Mayes," said FBI Special Agent Joel Siskovic, addressing whether he thought the two girls are alive.

At least 17 law enforcement agencies are involved and hundreds of people are working on the investigation, he said.

Siskovic declined to comment on a possible motive in the case and said the focus, for now, should stay on the missing girls.

Bobbi Booth, Teresa Mayes' sister, spoke to CNN's Anderson Cooper on Tuesday about Adam Mayes and his relationship with her sister, who she said has mental health problems.

"I've known Adam for at least 25 years, and he's always been weird and unusual ... but I never dreamed he would do something like this," she said.

She described him as aggressive and not trustworthy. He beat and threatened to kill her sister, said Booth, who pleaded with him through the interview to him to "do the right thing."

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"Just let the children go. This has gone on way too far. And we need to figure out what's going on, and it's not fair to the children," she said.

Adam Mayes, 35, is considered armed and dangerous, and authorities have asked for the public's help in tracking down him and the two girls.

In Mississippi, authorities continued to stop and search cars at checkpoints set up to look for them, state Highway Patrol Master Sgt. Johnny Poulos said.

"Everybody is tense," Peggy Guerry, who lives just a few houses away from the house linked to Mayes in Guntown, told HLN's Vinnie Politan.

"It's got everybody around here worried that he's still in the area, back in the woods or something like that," she said.

Authorities established contact with and tried to interview Mayes soon after the mother and her three daughters were reported missing on April 27 by Jo Ann's husband in Whiteville, a western Tennessee town of 4,600 people, but Mayes fled, Siskovic told CNN affiliate WPTY

He was last seen May 1 in Guntown, the same northern Mississippi town where the bodies were found. Details haven't been released as to how or exactly when they died.

The TBI late last week issued an Amber Alert asking for the public's help in finding the Bain sisters and for information leading to Mayes' arrest. Local, state and federal law enforcement's focus is now in Union County, Mississippi, where Guntown is located, but authorities have also pointed out that Mayes has connections to Texas, North Carolina, South Carolina and Florida and could be en route to Arizona.

Mayes may be using the alias of Christopher Zachery Wylde or Paco Rodrigass, his Facebook profile name, the FBI said Monday.

Rick Foster, whose wife was a lifelong friend of Jo Ann Bain and whose daughter was a classmate of Adrienne Bain, recently told CNN that Mayes had been a friend of the Bain family for years. Mayes lived about 90 miles away in Mississippi, Foster said, but would stay with the Bains when he was in the Whiteville area.

He described Mayes as "a big kid in a grown man's body."

Mary Patterson, Mayes' landlord in Alpine, Mississippi, told WPTY that she thought he was a "kind" and "fun guy."

"If somebody told me this, I would have never believed it," she said.

Authorities describe Mayes as a white man who has blue eyes and brown hair, weighs about 175 pounds and stands 6-foot-3. He recently cut his own hair and may have done the same to the missing children, according to the Amber Alert.

As for the Bains, Foster described the marriage between Jo Ann and her husband, Gary, as "perfect" and said the family had planned to move to Arizona once the school year ended.

The FBI and U.S. Marshals Service are offering a $50,000 reward for information leading to Mayes' arrest and to the missing girls.