There is no third degree murder. First degree is premeditated murder as well as murders occurring during the commission of other felonies. Second degree murder is all other murder.
1st degree murder is the willful, premeditated and deliberate unlawful killing of a human being with malice. 2nd degree murder requires malice but not premeditation and deliberation. There are defenses to these charges that your cousin's lawyer will discuss with him: self-defense for example. There is a limit to how far such a defense will go and if the self-defense was unjustified or excessive or if the killing were committed in the heat of passion the murder charge may be reduced to voluntary manslaughter.
1st Degree Murder: 25 to life, or if special circumstances exist, death;
2nd Degree Murder: 15 to life.
Voluntary manslaughter: 3, 6 or 11 years.
Note that if a weapon was used such as a firearm these penalties can be significantly increased.
Just because the district attorney charges a particular California Penal Code section, doesn't mean the district attorney will necessarily get a conviction. This could be a second degree murder case or possibly manslaughter, which is what you probably think third degree murder is (or isn't). There are defenses too. Your cousin will have to talk with his lawyer to discuss his options. We are presumed innocent until proven guilty.
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