I can't see there is any dispute about the fact that this was a professional job - for reasons that we will never know.
The strage element to this is the overkill - not just killing the target, but his wife, mother-in-law and 2 kids in such a way. Just whacking the bloke would have been a far simpler, clinical job - long range rifle, jobs a good 'un. Spraying a car with automatic gunfire and blowing away a witness sugguests there is far more to the killing than simply removing an risk or tidying up an inconvenience.
That was sending a message. Whoever/whatever the guy was involved with, the perpetrator (Mossad, CIA, MI6, The Moonies, whoever) has made it clear to anyone else involved that it is a poor idea to continue.