Early on a June morning in 2007, a family of five from Oswego, Illinois, had piled into their red Ford Expedition for a surprise trip to a water park three hours away. They never made it. A motorist found the father, Chris Vaughn, limping and disoriented, along the highway a short while later with gunshot wounds to his wrist and leg. His wife, Kimberly Vaughn, and their three children had been shot dead in the SUV, parked a little ways away. The murder weapon lay at Kimberly’s feet.

In 2012, an Illinois court convicted Vaughn of murdering Kimberly and their three children. The prosecution said he had shoved the gun under his wife’s chin and killed her first, before turning to the children in the back seat. The oldest, Abigayle, 12, was killed first, the state said. She died holding a stuffed animal and a Harry Potter book. Then Cassandra, 11, and finally Blake, 8, who authorities said had raised his arms in self defense.

Murder in Illinois, a new podcast from iHeartMedia, digs into this tragic case, intent on probing the possibility that Vaughn, who is serving multiple life sentences for the murders, is actually innocent.

Lauren Bright, who co-hosted Happy Face, about the daughter of Canada’s Happy Face Killer, hosts the 12-part series. She speaks with a private investigator, a journalist who covered the case, and members of Vaughn’s defense team, and Vaughn’s parents, siblings and other relatives, all of whom are speaking publicly for the first time about Chris’s conviction. They argue the State’s case for how the murder happened didn’t match the crime scene, that Vaughn was given an unfair trial, and that emotion over the horrific nature of the killings led to a biased outcome.

The uncomfortable part, of course, is that the only other possible killer seems to be Kimberly, whose family has so far declined to speak with the podcast creators. Murder in Illinois address this on the first episode, and argue that the chance of an innocent man rotting in jail is worth the pain of questioning the outcome of the case.

“What happened in the Vaughn family’s SUV was unfathomable,” Bright says on the episode. “Three innocent children died facing a gun that was held by one of the last people they ever thought would harm them. But the only thing that could make this tragedy any more disturbing is the possibility that the man serving life sentences for having taken those lives didn’t actually commit the murders.”