The medical examiner (ME), when dealing with death, is charged with determining the cause and manner of death. The cause is what actually led to the death; the manner is by whose hand and for what purpose the death occurred. These manners can be natural, accidental, suicidal, homicidal, or undetermined, the latter being designated when the ME can't assign the death to one of the other manners with any degree of certainty.
The determination of the manner of death is not always easy and in some situations can seem odd. For example, can someone die from pneumonia yet the cause of death be homicide? How does a killer give someone pneumonia?
Say a thief shoots a store clerk during the course of the robbery. The clerk survives but is paralyzed from the neck down and ultimately is placed in a neurological treatment center where such injuries are cared for. He is bedridden and dependent on the staff for everything from eating to bathing to changing positions in bed. Someone in this situation can linger for many years with proper care. The most frequent cause of death in such cases is an infection such as pneumonia, a urinary tract infection, or an infection in a bed sore (decubitus ulcer), which is caused by localized pressure from lying in one position too long. Each of these infections can seed the bloodstream and cause septicemia (infection in the bloodstream), which carries a high mortality rate. Say the clerk lives for 20 years but ultimately develops pneumonia and dies.
What's the manner of death? Pneumonia is a natural cause of death so the manner must be natural, too. Right? Not necessarily. If the victim were not paralyzed and confined to bed, he likely would not have developed his fatal pneumonia as this is much rarer in healthy ambulatory people. So the pneumonia arose from his paralysis, which in turn occurred at the hand of the thief who fired the shot. So the shooting began the "cascade of events" that led to the victim's death. The manner of death could easily be deemed homicidal in this situation. And many cases have followed just such a pattern.
In 1994, Scott Sittler was shot in the head in Santa Ana, California, and the resulting injuries left him quadriplegic. In 1996, Erwin Johnny Sanchez, his brother Giovanny Edgar Sanchez, and friend Daniel Paul Cruz pled guilty to attempted murder and were carted off to prison. But in 2009, Sittler developed pneumonia and died. The ME listed the manner of death as homicide, opening the door for murder charges against the three men.