(CNN) French police investigating an anesthesiologist in connection with multiple poisonings have added 17 new cases to their probe.

Frederic Pechier, 47, was previously charged in 2017 in relation to seven cases of poisoning, public prosecutor Etienne Manteaux told reporters at a televised press conference Thursday, with the 24 total cases resulting in nine deaths.

Pechier worked at two private clinics in Besançon, eastern France.

Pechier worked in two private clinics.

Investigators allege that he tampered with medical equipment so colleagues would administer dangerously high levels of local anesthetic or potassium to patients aged between 4 and 80 who were undergoing minor operations.

When the patients went into cardiac arrest as a result, Pechier would step in to revive them and show off his apparent skill as a doctor, investigators allege.

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