On April 29, 2004, Cullen pleaded guilty to murdering 13 patients and attempting to kill two others as part of a deal with prosecutors to spare his own life.

Most of the victims' families didn't realize at the time that the deaths weren't from natural causes, because the victims were often seriously ill. Prosecutors have said Cullen claimed he gave the patients lethal drug overdoses to end their suffering.

According to the agreement with prosecutors, he faces consecutive life terms for the murders with no eligibility for parole for more than 120 years.