He did not inrend to kill.
Legally, one can impute "intent" from actions. It's called a "legal fiction" and is done all the time.
If you behave in an especially reckless manner, and kill someone, intent to kill can be inferred even if you didn't have "actual intent."
Second Degree Murder and Involuntary Manslaughter are two crimes where reckless behavior can create legal intent even if you did have "actual intent."
The Marine's behavior might be regarded as reckless by a jury. The degree of recklessness will determine whether (or if) he's found guilty of Involuntary Manslaughter or Second Degree Murder.