In Common Law, murder is homicide committed with malice aforethought. Usually, every intentional killing is with malice aforethought unless there was some sort of justification, excuse or other mitigation.

California Criminal Law

       Murder, in California, is defined as the unlawful killing of a human being, or a fetus, with malice aforethought. Specifically excepted out from the definition is the killing of a fetus pursuant to an abortion under the Therapeutic Abortion Act, or if the death of the fetus was solicited, aided, abetted or consented to by the mother of the fetus.
Malice can be either express or implied. It is express when it is an intentional killing. It is implied when there is insufficient provocation or when the act is evidence of an abandoned and malignant heart.

       California, has two basic types of murder. They are first degree murder and second degree murder.

First Degree Murder

       First degree murder is the unlawful killing of a human being or a fetus, with malice, either express or implied, that is willful, deliberate and premeditated. Under the felony murder rule, certain other murders that occur during the perpetration of burglary, robbery, rape, carjacking, arson, mayhem, kidnapping and other listed crimes, are first degree. What is significant about the felony murder rule is that no malice is required. The penalty for first degree murder is death, life without the possibility of parole or a term of 25 years to life.

Special Circumstances

       In order for a jury to find death, they must find the existence of a special circumstance. The same jury that hears the guilt phase of the trial will be the jury that hears the penalty phase. Currently there are about 35 different "special circumstances" listed in Penal Code §190.2. If the jury finds one or more special circumstances, then the penalty phase starts. The jury decides whether the penalty should be death or confinement in state prison for life without the possibility of parole. The death penalty cannot be imposed on anyone who was under age 18 at the time of the commission of the crime or those who are suffering from sufficient mental deficiencies.

Second Degree Murder

       Generally, all other murders are of the second degree. Unless the victim was a peace officer, the punishment is 15 years to life.
California also punishes attempted murder. The punishment for attempted willful, deliberate, and premeditated murder is life in prison. All other attempted murders are punishable by five, seven or nine years.