KALAMAZOO, Mich. (WOOD) — The FBI is offering a reward of up to $20,000 for information that leads to the location of a missing mother of eight. Law enforcement believe the woman, Heather Kelley of Michigan, has been killed.

Kelley, 35, has been missing since December. Her car was found burning the next day. Once the fire was out, investigators found her blood and human hair in it.

When Kelley left home, she told her kids she was going to see her boyfriend, who was serving time at a halfway house. Court records show the boyfriend’s electronic tether went dead the night Kelley was last seen. He later ran away from the halfway house.

Nexstar is not naming the boyfriend because he has not been charged in relation to Kelley’s death.

The 37-year-old man has now been indicted on a federal charge of escaping a halfway house.

He was scheduled to be released from federal custody on April 26, but the new escape charge means law enforcement can continue holding him, giving police in Michigan’s Kalamazoo County more time to investigate.

Search warrants show the man was serving out the end of a federal cocaine sentence at KPEP, a halfway house in Kalamazoo. The warrants also show that at 9:30 p.m. on the day of Kelley’s disappearance, his electronic tether went dead.

Jennifer Toon, a Texas criminal justice activist who served time in prison and on a tether at a halfway house, said it’s not unusual for tether batteries to die. They need recharging daily.

“So if it goes dead, then you haven’t been charging it,” said Toon, project director of Lioness: Justice Impacted Women’s Alliance in Texas.

In Texas, a dead battery immediately sends a notification to those who monitor the tethers, she said.

“All it would have taken is a supervising officer or a command center immediately to call the halfway house and say, ‘So-and-so’s battery is dead, put eyes on him.’ That’s what happens with us in Texas,” Toon said.

But a spokesman for the halfway house in Michigan, John Truscott, said that’s not what the contract with the Bureau of Prisons calls for.

“A tether is to determine for the Bureau of Prisons how a person is complying with their rules,” Truscott said. “It’s not meant for an instantaneous response to law enforcement. Just because a tether loses its charge, it’s not a law enforcement violation. There’s no reason to activate law enforcement, and frankly with how stretched they are these days, they wouldn’t go after them anyway.”

The tether went dead, court records show, about the same time Kelley was calling her kids to say she was meeting her boyfriend in Kalamazoo. Phone records show they were together that night at a Kalamazoo dinner club where the man worked.

He returned to the halfway house early the next morning with what a roommate described as deep scratches on his chest and back, court records show.

Just before 6 a.m., the tether was back on. Police said they believe Kelley was killed and her body disposed of during that 8.5-hour window.

Police are investigating Kelley’s case as a homicide, even though they haven’t found her body.

After her car was discovered with her blood in it, the man ran from the halfway house and cut off his tether, search warrants show. He was arrested several days later.

A spokesman for the Federal Bureau of Prisons in Washington, D.C., refused to discuss the case with Nexstar’s WOOD.

“For privacy, safety, and security reasons, the Bureau of Prisons (BOP) does not comment on matters related to pending litigation, ongoing legal proceedings, or ongoing investigations,” spokesman Donald Murphy said.

“I can tell you, KPEP did everything they were supposed to do in this case,” Truscott, the KPEP spokesman, said. “They also, when a tether goes out, will call and follow up to make sure a person is where they’re supposed to be at that given time. That is standard practice and everything was complied with in this case.”

Anyone with information about the case or where Kelley may be is asked to call Portage police at 269-329-4567, the Kalamazoo County Sheriff’s Office at 269-383-8748 or the FBI Detroit Field Office at 313-965-2323.

Editor’s note: The CEO of KPEP is the spouse of a WOOD employee. That employee was not involved in preparing this report.