While working as a nurse, Cullen murdered dozens—possibly hundreds—of patients during a 16-year career spanning several New Jersey and Pennsylvania medical centers until being arrested in 2003.

The following year, Cullen graduated from West Orange High School and enlisted in the United States Navy.

He successfully passed basic training and the psychological examinations required for submarine crews (who were expected to spend as long as two months at a time being submerged in a cramped vessel).

Cullen rose to the rank of petty officer second class as part of the team that operated the vessel's Poseidon missiles.

[citation needed] A year into his service, Cullen's leading petty officer aboard Woodrow Wilson discovered him seated at the missile controls wearing a surgical mask, gloves, and scrubs rather than his uniform.

Elected president of his nursing class, he graduated in 1987[7] and started work at the burn unit of Saint Barnabas Medical Center in Livingston, New Jersey.

[4] Cullen left Saint Barnabas in January 1992 when the hospital authorities began investigating the contaminated IV bags.

[4] One month after leaving Saint Barnabas, Cullen took a job at Warren Hospital in Phillipsburg, New Jersey, where he murdered three elderly women with overdoses of the heart medication digoxin.

Cullen later claimed that he had wanted to quit nursing in 1993, but the court-ordered child support payments forced him to continue working.

That September, a 91-year-old cancer patient at Warren Hospital reported that Cullen, who was not her assigned nurse, had come into her room and injected her with a needle.

Her son protested that her death was not natural, and the hospital administered a lie detector test to Cullen and several other nurses, which he passed.

[citation needed] Cullen began a three-year stint in the intensive care unit of Hunterdon Medical Center in Flemington, New Jersey.

In February 1998, Cullen was hired by the Liberty Nursing and Rehabilitation Center in Allentown, Pennsylvania, where he staffed a ward of respirator-dependent patients.

Even with his history of mental instability and the number of deaths during his employment at various hospitals, Cullen continued to find work because of a national shortage of nurses.

On January 11, 2000, he once again attempted suicide by lighting a charcoal grill in his bathtub and hoped to succumb to carbon monoxide poisoning.

In September 2002, Cullen began working in the critical care unit of the Somerset Medical Center in Somerville, New Jersey.

On June 18, 2003, he unsuccessfully attempted to murder Somerset patient Philip Gregor, who was later discharged and died six months later of natural causes.

In July 2003, the executive director of the New Jersey Poison Information and Education System warned Somerset officials that at least four suspicious overdoses indicated the possibility that an employee was killing patients.

When a patient in Somerset died of low blood sugar in October 2003, the hospital alerted the New Jersey State Police.

State officials castigated the hospital for failing to report a nonfatal insulin overdose administered by Cullen in August.

[11] As part of his plea agreement, Cullen promised to cooperate with authorities if they did not seek the death penalty for his crimes.

As part of his plea agreement, Cullen has been working with law enforcement officials to identify additional victims.

[2][4] Cullen stated that he had overdosed patients to spare them from being seen going into cardiac or respiratory arrest and being listed as a Code Blue emergency.

Similarly, Cullen told investigators that although he often observed patients' suffering for several days, the decision to commit each murder was performed on impulse.

Cullen told detectives in December 2003 that he lived most of his life in a fog and that he had blacked out memories of murdering most of his victims.

[19] Prompted by the Cullen case, Pennsylvania, New Jersey, and 35 other states adopted new laws which encourage employers to give honest appraisals of workers' job performance and provide legal protections for reporting medical errors.

[18] The 2008 direct-to-video film Killer Nurse, written and directed by Ulli Lommel, was loosely based on Cullen.

[20] The CBS newsmagazine show 60 Minutes featured an interview with Cullen conducted by correspondent Steve Kroft, in an episode which originally aired on April 28, 2013, and which was titled "Angel of Death".

[21] On June 25, 2020, the British television channel Sky Crime aired the documentary Charles Cullen – Killing for Kindness, produced by Woodcut Mediastory.

There are interviews with family members of the victims, true crime author Charles Graeber and audio from Cullen himself.