homicide is always a crime since its the unlawful kiling of another person, what differs is what can be proven, and what can be prosecuted when it comes to court

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not sure how its legally defined in other countries but in the U.K. it is to do with intent

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did the person wait in a bush outside victim's house, with a gun, and jump out and shoot man when he got home from work (predetermined, intent) (murder)

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or did man get home early from work, walk in on next door neighbour balls deep in his wife (discovered affair), pick up lamp off it's position on bedside table and smash him on the head (in the moment) (manslaughter)

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some countries the manslaughter ting there could even be argued as a crime of passion and wouldn't even be manslaughter

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and then there is also conspiracy, where one mans crime becomes every mans crime (for example gangs)

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you could be sent to prison for murder just for driving a car through the acts of a passenger (for example a shooting drive by, passenger kills man, you were driver, you also are responsible for the crime and therefore cop a murder charge)