When a patient in Somerset died of low blood sugar in October 2003, the hospital alerted the New Jersey State Police. That patient was Cullen's final victim. State officials castigated the hospital for failing to report a nonfatal insulin overdose, administered by Cullen, in August. An investigation into his employment history revealed past suspicions about his involvement in patient deaths. Somerset fired Cullen on October 31, 2003, ostensibly for lying on his job application. Fellow nurse Amy Loughren alerted the police after becoming alarmed about Cullen's records of accessing drugs and links to patient deaths. Police kept him under surveillance for several weeks, until they had finished their investigation. Investigators assigned Loughren to visit Cullen after work hours and talk with him while wearing a wire. From this, they were able to produce enough evidence for probable cause of arrest.