A nurse is facing multiple charges of administering lethal or potentially lethal doses of insulin to 22 patients at several health care centres across Pennsylvania.
Heather Pressdee was charged on Thursday with two counts of first-degree murder, 17 counts of attempted murder and 19 counts of neglect of a care-dependent person, the Pennsylvania Attorney General's Office said.
The 41-year-old was already facing charges of killing two nursing home patients and injuring a third, which were brought in May.
Pressdee allegedly gave excessive doses of insulin to the patients - some diabetic and some not - over the last three years.
In total, 17 patients cared for by Pressdee died, Attorney General Michelle Henry said. The nurse was charged with first-degree murder in the cases for which physical evidence was available to support the cause of death, and attempted murder where patients survived or a cause of death could not be established.
The patients who died ranged in age from 43 to 104.
Insulin was typically administered during overnight shifts when staffing was low and the emergencies would not immediately result in patients being taken to hospital, Ms Henry said.
"The allegations against Ms Pressdee are disturbing," she added. "It is hard to comprehend how a nurse, trusted to care for her patients, could choose to deliberately and systematically harm them."
The nurse's lawyer told Sky News' US partner NBC News that their goal was to avoid the death penalty.
Read more from Sky News:
Ex-gang leader denies orchestrating Tupac's murder
Woman accused of murder 'tracked cyclist on Strava'
According to court documents, Pressdee sent her mother numerous texts between April 2022 and May of this year in which she discussed her unhappiness with various patients and colleagues and spoke about potentially harming them.
She also voiced similar complaints about people she met at restaurants and other places outside of the care facilities where she worked, authorities said.
Charging documents from May said Pressdee had a history of being "disciplined for abusive behaviour towards patients and/or staff at each facility resulting in her resigning or being terminated".
She held a number of jobs at nursing homes and facilities in western Pennsylvania beginning in 2018 for short periods of time, according to the documents.
Pressdee remains in custody at Butler County Prison, without bail.