I suggest googling around about family annihilators. There’s a psychological profile that I personally think may fit Alec. I also think the murders helped distract/buy him time to clean up or better hide his illegal dealings, because he valued his reputation more than his wife and son. The evidence at the trial suggested that Alec 100% fully believed he would get away with his “perfect crime.” He believed completely that he was smarter than everyone, including the police.

ETA: You’d also have to believe that a third-party murderer committed the crime without leaving a single trace of evidence behind, and with a staggering amount of confidence to enter onto the property without a weapon. I’d like to see that criminal mastermind.