Why do people always think that crime is committed by PROFESSIONALS?
I don't think that people "always" think that.
I certainly don't always think that.
But with this crime in particular you've got an entire family more or less wiped out in what law enforcement is calling "execution style" killings.
You've got illegal marijuana grow operations at three of the four murder locations.
You've got illegal dog fighting and **** fighting operations at least one of the locations.
You've got early morning killings, which could be indicative of the perpetrators' knowledge that early morning is the time of day when people are naturally at their least guarded.
You've got neighbors who were awake, and in close enough proximity that they would have heard multiple gunshots breaking the early morning silence, claiming that they heard nothing out of the ordinary that morning, indicating the use of suppressors.
There has been (not unreasonable) speculation in the media, and I don't think anyone would be surprised at the end of the day to learn, that the Mexican mafia or one of the cartels was somehow involved in all of this.
So, as I've said, while I do not think all murders, or all crimes more generally, are professional, I do think that this case has enough hallmarks of a gangland/drugland type event that folks can be forgiven for thinking that maybe what evidence we are aware of might be pointing in that direction.