American serial killer Gary Ridgway pleaded guilty to 48 counts of first-degree murder.

Gary Leon Ridgway, known as the Green River Killer or the Green River Strangler, is an American serial killer who was convicted of murdering forty-nine women between 1982 and 1998 in the northwestern United States. At the time of his arrest in 2001, he was believed to be the most prolific serial killer in United States history, according to confirmed murders.

In the United States, the law for murder varies by jurisdiction. In many US jurisdictions there is a hierarchy of acts, known collectively as homicide, of which first-degree murder and felony murder are the most serious, followed by second-degree murder and, in a few states, third-degree murder, which in other states is divided into voluntary manslaughter, and involuntary manslaughter such as reckless homicide and negligent homicide, which are the least serious, and ending finally in justifiable homicide, which is not a crime. However, because there are at least 52 relevant jurisdictions, each with its own criminal code, this is a considerable simplification.