Sophisticated X-ray body scanners that could curb widespread smuggling of scalpels and razors at New York City’s notorious Rikers Island jail have sat unused for years, thanks to a state law barring such devices that emit low doses of radiation.

The city must use weaker metal detectors that investigations have shown can allow blades to slip through if they are simply wrapped in duct tape.

A city report issued in February said more than 2,200 weapons were recovered inside city jails last year and that the number of slashings and stabbings at city jails rose 66% from the prior year.

“It’s absurd,” said city councilwoman Elizabeth Crowley, who chairs a legislative committee overseeing the correction department. “They have these scanners and they paid a lot of money for these scanners and they’re not getting used.”

City officials say they purchased the seven airport-style body scanners in 2012 and 2013 for more than $1m, putting them in operation at the jail complex for about a year before they learned of a state law that prohibits nonmedical uses of machines that emit small doses of radiation. Federal law allows similar scanners to be used at airports and in some federal prisons.

Joseph Ponte, the department of correction’s commissioner, told legislators at a budget hearing last year that the machines, which were the subject of a handful of lawsuits by prisoners at Rikers, were pulled from service in early 2014. Since then, they have sat in storage while the city lobbied lawmakers to try to pass legislation that would allow them to use the machines.

“They cite some law, but I don’t know that any lawsuit or judge would say that the department is hurting somebody’s physical wellbeing by allowing these scanners to be used,” Crowley said. “I personally think they should use them with or without the state law.”

The majority of screening points at the 10 Rikers’ jails are equipped with walk-through metal detectors, known as magnetometers. But the commissioner of a city agency that has led a sprawling investigation into corruption in the city jail system says the machines can be easily tricked and have repeatedly failed to catch people who admitted smuggling weapons.

“There’s no comparison,” said Cameron Lindsay, a former federal prison warden who now works as a jail security consultant. “The body scanners are much better. The technology is exponentially better, and you can see the entire person’s body without strip-searching them.”

In November, a correction officer was slashed across the face by an inmate wielding a scalpel and needed more than two dozen stitches to close the wound.

A Rikers Island correction officer was indicted last month after authorities said he smuggled seven scalpels inside a package of synthetic marijuana, wrapped with duct tape. The officer, Kevin McKoy, had told investigators he had been able to smuggle scalpels into the jail previously by walking through the magnetometers undetected, said Mark Peters, the commissioner of the department of investigation.

McKoy has pleaded not guilty. His attorney has declined to comment on the case.

In 2014, a department of investigation probe found that an undercover investigator was able to smuggle a razor blade into the jails on Rikers Island in each of six attempts.

Ponte said the correction department was “taking aggressive steps to stem the flow of contraband”, including increasing visitor searches and overhauling the process for recruiting correction officers.

The city says it has purchased 10 new scanners designed to catch cellphones that may be smuggled into the jail and officials say those machines are also helpful in finding small wrapped weapons.

The city’s top financial officer said the purchase of the body scanners was “an example of how a lack of due diligence can cost taxpayers money”.

“The department of correction doesn’t have to put these X-ray scanners up on eBay, but there’s no point in having them sit there and depreciate down to nothing,” New York City comptroller Scott Stringer said.

Norman Seabrook, president of the union that represents correction officers, said union officials needed to learn more about the body scanners to verify there are no health risks to officers who may be posted at the scanners every day.