The FBI is investigating a surgical device that was found to spread cancer in women, including looking into what the largest manufacturer of it, Johnson & Johnson, knew about the tool’s hazards before pulling it off the market last year, according to people who have been interviewed by the agency.

It is unclear what stage the inquiry is in. The Federal Bureau of Investigation’s Newark, N.J., office, which is overseeing the investigation according to the three people interviewed, declined to comment. A J&J spokesman said the New Jersey-based medical company isn’t aware of an investigation into the device, called a laparoscopic power morcellator.

Over the past several months, FBI agents have interviewed a retired pathologist who alerted J&J about potential problems with morcellators in 2006; a doctor who went public after her own cancer was worsened by the tool in 2013; and a California woman who has collected names of close to 400 patients and families of patients who may have been harmed by the tool, these people said.

The probe comes after the U.S. Food and Drug Administration warned in November that morcellators shouldn’t be used on the vast majority of women.

Many hospitals and the nation’s largest health plans either have curtailed use of morcellators or are considering limits.

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