(CNN) -- Adam Mayes -- accused of murder and kidnapping in a case involving a Tennessee mother and her three daughters -- has died, FBI spokesman Joel Siskovic said late Thursday. The two sisters he allegedly kidnapped were found alive, law enforcement sources said.
There had been conflicting reports about whether Mayes was dead or alive after he reportedly shot himself in Union County, Mississippi.
Daniel McMullen, FBI special agent in charge in Jackson, Mississippi, said that officers with the Mississippi Highway Safety Patrol and state Department of Fisheries, Wildlife and Parks rescued Alexandria and Kyliyah Bain, "alive and unharmed."
"Preliminary reports indicate that Mr. Mayes shot himself in the head and was later pronounced dead," McMullen told reporters.
The two surviving sisters "are suffering from the experience of being out in the woods and from being kidnapped. They are suffering from dehydration and exhaustion, but appear OK," a federal law enforcement source on the scene told CNN.
Mayes, 35, was suspected of abducting Alexandria, 12, and Kyliyah, 8, from their Whiteville, Tennessee, home, in late April, and killing Jo Ann Bain and her eldest daughter, Adrienne, 14.
The FBI on Wednesday put Adam Mayes on its list of 10 most wanted fugitives. The reward for information leading to Mayes' arrest stood at $175,000 on Thursday.
Authorities responded Thursday evening after someone called to report what they believed may have been Mayes' vehicle, a law enforcement source close to the investigation said.
A task force was nearby and as they approached, Mayes stood up and shot himself in the head, the source said. The two girls were not near him at the time.
Mayes and his wife, Teresa Mayes, had been charged with two counts of first-degree murder and two counts of especially aggravated kidnapping. He faced an additional count of making a false report, according to arrest affidavits filed in Tennessee.
Adam Mayes' mother-in-law told HLN's Nancy Grace on Thursday that he may have believed he was the father of the two young girls he was accused of abducting.
"He believes they are his children," Josie Tate told Grace.
Tate, who lives in Chatsworth, Georgia, tearfully pleaded for Mayes to return Alexandria and Kyliyah Bain and turn himself in.
"You've had a chance to live life. They haven't," Tate said. "Give them that chance."
Police said Teresa Mayes told them she was in the Bains' garage when Adam Mayes killed Jo Ann and Adrienne Bain.
Teresa Mayes' lawyer, Shana Johnson, said Thursday that her client last saw Mayes and the Bain girls in Mississippi on April 27.
The Mayes family and the Bain family are connected through Adam Mayes' sister Pamela, who used to be married to Jo Ann's husband, Gary Bain, the lawyer said.
Johnson told HLN she was "happy" and "relieved" the girls had been found alive.
In affidavits, investigators said the Mayeses drove the bodies of Jo Ann and Adrienne Bain to Union County in northern Mississippi, where they were discovered Saturday in a shallow grave behind the house of Adam Mayes' mother in Guntown, Mississippi.
Adam Mayes' mother, Mary Frances Mayes, has been charged with four counts of conspiracy to commit especially aggravated kidnapping.
Adam Mayes was last seen May 1 in Guntown. While the search was centered around his hometown, he also had connections to Arizona, Texas, Florida and the Carolinas, the FBI said.
Bobbi Booth, Mayes' sister-in-law, told CNN's Anderson Cooper on Thursday night that she's "overwhelmed right now."
"All I'm (thinking) about now is that the children are safe," said Booth. "Thank you, God, for letting those children come home."
Booth described Adam Mayes as "aggressive, abusive, crazy obviously."
But Booth said she never had an inkling Mayes would be accused of kidnapping and murder.
"I never dreamed that he would do this," she said.
CNN's Rich Phillips and Joe Sutton, and HLN's Natisha Lance, Mike Brooks and Josey Crews contributed to this report.