One of the last remaining checks on Immigration and Customs Enforcement and private-prison contractors running immigration detention centers has all but collapsed, leaving thousands of people trapped in a system with nearly non-existent oversight.

The grievance system in immigration detention is designed to offer a safe channel to report violations of detention standards and seek redress, without fear of retaliation. It's often the only recourse for people to submit complaints about detention issues, including mistreatment, unsanitary conditions, medical neglect, and sexual assault. But an NPR review has found the system — which in the best of times was a complex patchwork — barely operates and even at times backfires for those using it. It is one of the few remaining safeguards for immigrants in federal custody after the Trump administration effectively dismantled other oversight offices.

Detainees and their families tell NPR that in the very worst cases the absence of transparency and accountability, and the subsequent failure to adhere to mandated grievance guidelines is one of the leading factors for the record number of deaths in detention — at least 53 since the start of President Trump's second term.

Critics say it is the reason why more detainees are risking their lives to protest inhumane conditions and legal rights violations, in the form of widespread hunger strikes.

The Department of Homeland Security declined to answer specific questions about how it handles detainees' grievance claims, how DHS or private contractor employees are trained, what steps it takes to ensure private contractors — the largest being CoreCivic and The GEO Group — adhere to guidelines, or whether all detention facilities have a mandatory grievance committee. Instead, the office referred NPR to the 2011 Performance-Based National Detention Standards, which outlines how the system is intended to work.

That system didn't work for D.E., who has had a brain tumor growing in his head for the last 12 years.

He was supposed to start chemotherapy the week he was picked up by ICE just a couple blocks from his home.

The first seizure in detention was terrifying, but the second was the worst.

It was around 2 a.m. and D.E., one of more than a thousand detainees in the California City Detention Center, was lying on the lower bunk of his small cell. The CoreCivic guard who normally brought his nightly dose of Keppra, the medication he's relied on twice a day for years to keep seizures at bay, was more than five hours late, and it wasn't the first time. He'd had the first seizure just a couple of weeks earlier and the telltale signs of an oncoming convulsion were in full effect: A relentless throbbing in his brain behind the three inch scar above his left ear. The blurred vision. The dizziness.

"I could feel it coming and I didn't want to hurt myself so I jammed my arm between the metal bed frame and the wall to lock myself in place," D.E., a Mexican national who requested NPR only use his initials because he fears government retaliation, said in Spanish. Trapping his arm was the best precaution he could come up with to keep himself from accidentally falling face first into the shared toilet that was just inches from his bed, he said. "It's what I was most afraid of because I could have drowned."