Furman v. Georgia

In 1794, Pennsylvania became the first state to establish a legal distinction between first-degree murder--that is, "willful, deliberate, or premeditated killing"--and a second degree of murder charges, in which the defendant was judged to be less culpable due to a lesser intent or other mitigating circumstances.

Since that time, other states have adopted their own standards of first-degree (or capital) murder on the basis of a variety of circumstances. Some of the factors involved in the determination of first-murder in various states are the use of torture; murdering for financial gain; killing a police officer or other public official; killing during the commission of a felony such as rape, robbery, kidnapping, or the performance of a sexual act with a person under the age of fourteen; use of an explosive; a prior record for murder; and murder that involves--to use a phrase from the 1794 Pennsylvania statute--lying in wait for the victim.

Just as misdemeanors are generally understood as that class of crimes which are not classified as felonies, so second-degree murder is usually any type of murder that does not qualify as first-degree.