Nine mysterious deaths have long perplexed a Missouri hospital wondering what caused them. Two decades later and now the answer may be a grim one after a former nurse has been arrested for murder.

On Thursday, police in rural Livingston County in Missouri arrested Jennifer Anne Hall, a former nurse at Hedrick Medical Center where all of the deaths took place. In 2002, Hall worked for five months as a respiratory therapist at the hospital when the deaths occurred and authorities say that they believe she is responsible for murdering at least one of the patients.

Ten years ago, Livingston County Prosecuting Attorney Adam Warren launched an investigation into the 2002 death of 75-year-old Fern Franco at the hospital, where he died from what Warren said was a lethal overdose on succinylcholine - a relaxant that paralyzes the respiratory muscles - and morphine.

This overdose, according to authorities, was administered by Hall when she was employed at Hedrick Medical Center.

Hall has already pleaded not guilty in the killing of Franco, the only death from 2002 that she is being charged with. Despite this, police noted in their probable cause statement for Hall’s arrest that cardiac arrests at the hospital “rose alarmingly” during the period that she was employed there.

Officials at Hedrick were reportedly alerted to concerns about Hall and she was suspended after Franco's death for three days, which brought down the number of cardiac incidents, according to police.

However, she was not fired by the hospital until months later after she was convicted on arson charges at another hospital nearby.

Hall’s attorney, Matt O’Connor, accused law enforcement and the hospital of scapegoating Hall for the deaths because of the arson conviction, a charge she was acquitted of in 2005. By charging her for the murder of Franco, O'Connor said that it was "unfathomable" that his client would be accused of murder now.

“To go through it once is terrible,” O’Connor said. “To go through it twice is a recurring nightmare.”