Over the summer, after some 15 years, the Trump administration announced the federal government would reinstate capital punishment. A federal judge in Washington, DC, however, last week halted that plan, blocking four scheduled executions. The Justice Department filed a request to stay the decision, and says it plans to appeal.

Yet de facto capital punishment continues to exist for one specific violation, at least for the inmates at an undisclosed number of federal prisons: Attempted escape.

Earlier this month, the federal government issued a solicitation for bids from contractors to refurbish a so-called “lethal/non-lethal” fence around a federal correctional facility in Tucson, Arizona. Three bids have so far been submitted, ranging from $3.3 million to about $3.8 million. One of the companies, KWR Construction, has been involved in constructing prototypes for US president Donald Trump’s long-promised, and highly controversial, border wall.

A lethal/non-lethal fence is an electrified fence running around the perimeter of a prison. Upon first contact, these fences deliver a non-lethal electric shock, but a second one triggers a lethal high-voltage discharge, typically several times more powerful than a standard electric chair. This is meant to kill the potential escapee on the spot.

Bureau of Prisons An electrified fence at FCC Tucson.

“Lethal force is authorized to prevent inmate escapes,” said Justin Long, a spokesperson for the US Bureau of Prisons, the agency that oversees the federal correctional system. Long declined to provide Quartz with the precise number of federal facilities now equipped with lethal electric fences, but said it’s “more than seven.”

A majority of US states, meanwhile, still have the death penalty, though few actually carry out executions. And like their federal counterparts, a number of state prisons are surround by non-lethal/lethal electric fencing. In California, where governor Gavin Newsom in March declared a moratorium on executions, about two dozen state prisons are equipped with the deadly fences. Electric prison fences in California deliver 5,000 volts of electricity to inmates trying to escape. In Missouri, the fences mete out 5,100-volt shocks.

“As a comparison, most electric chairs employ a shock of between 1,700 and 2,400 volts for 30 to 60 seconds to produce a lethal current,” wrote Milo Miller, a former researcher at Southwest Missouri State University, in a paper published in 2001 in the California Western Law Review.

Many states allow for the use of “deadly force” to thwart an escape attempt, but limit its use to situations where the officer “reasonably believes it necessary” to prevent or terminate the escape.

“The use of firearms or other means of deadly force in a particular situation, by its nature, calls for the application of human judgment or discretion. Fences, unlike humans, cannot think, assess circumstances, or exercise judgment,” Miller wrote.

Lethal fencing began in the early 1990s as a way to save money. Some state prisons, including in Alabama, Arkansas, California, Nevada, and Missouri, have now used them for more than two decades. In California, the first lethal fence was installed in 1993. It was part of a program to install 19 electrified fences in order to save $42 million a year ($79 million today).

The Bureau of Prisons began plans to install lethal fencing in federal prisons in 2006 for the same reason. The fences meant less need for tower guards, who earn up to $70,000 per year at some prisons, with overtime, and generous pensions after they retire. Fences don’t.

A violation of international human rights law

The use of such fences is of concern to human rights advocates.

“Under international law, guards standing on towers—or any automated system—must weigh whether or not the use of lethal force is strictly necessary,” said Alison Leal Parker, director of US Programs at Human Rights Watch. In this, she told Quartz, “the use of lethal force under state and federal law in the US contradicts international human rights law.”

“There are times when technology can be rights-respecting and even rights-protecting in a way that human decision-making may be flawed,” she added. “But there are also many, many instances—and I would argue this is one—where the need to assess whether killing someone is strictly necessary cannot be done by an automated fence.”

That is, fences lack the key element of human judgement that would make the use of deadly force legal.

“The Eighth Amendment is what we would look at to see if [the fences] are legal,” said Nila Bala, an associate director for criminal justice and civil liberties at R Street, a nonpartisan public policy research nonprofit. The amendment forbids the use of “cruel and unusual punishment,” and the indiscriminate use of lethal force by an automated device would likely not pass this standard.

“This issue has never really reached the Supreme Court,” Bala told Quartz, though the court has ruled on the use of deadly force in correctional facilities. “The law is fairly deferential about what happens in correctional facilities,” she said, allowing for “good faith judgement” made by law enforcement officials, even when it results in the death of the inmate.

But an automated device is different, and its use should raise questions even from a policy point of view, as their function can deviate from the goal of deterring escapees. “Inmates could use the fence against each other,” Bala said, “or use them to commit suicide.” Further, she added, there are plenty of examples—both in the United States, and from other countries—showing there is no added advantage, in terms of safety, in using indiscriminate lethal force when lesser force would be effective.

Whether or not lethal/non-lethal fences adhere to the letter of the law is almost beside the point, said Nick Schwellenbach, director of investigations at the nonprofit Program on Government Oversight.

“This seems like a dramatic escalation of consequences without requiring human intervention,” Schwellenbach told Quartz. “While electric fences are a more pedestrian technology, this makes me think of the intense debate over drones that could kill without human oversight.”

Unintended consequences

It turns out that inmates aren’t the only ones under threat from these lethal fences. It’s other species that suffer the most.

“Mostly they kill birds and small animals,” Martin Horn, former commissioner of the NYC Department of Correction, told Quartz.

Indeed, the first five years after California installed lethal electric fencing in 1993 at 25 of its 33 state prisons, some 3,000 migrating birds were electrocuted, according to United States Fish and Wildlife Service data cited by the New York Times. They included 144 burrowing owls, 111 loggerhead shrikes, and 10 red-tailed hawks.

To Steven Van De Steene, a Belgian expert on the use of technology in correctional settings, a “dynamic” correctional model works best. That means focusing on creating a culture of rehabilitation, fostering trust between staff and inmates, and utilizing “non-security-related tools and technologies to create a safer environment,” he told Quartz.

“If you treat people like animals,” he said, “they will behave like animals.”