02/06/2012 at 02:50 PM EST
Chuck Cox says that the family told anybody who would listen: It was only a matter of time before his son-in-law Josh Powell killed himself and his two boys.
On Sunday, those worst fears were realized when Josh, long a person of interest in the disappearance of wife Susan Powell, blew up
his Tacoma, Wash.-area house in what is being characterized as a double-murder suicide.
"We stated our fear many times, that if he was feeling desperate, that he would possibly kill himself and the boys, that this kind of thing could happen," Susan's father Chuck tells PEOPLE. "If he felt there was no way out, that he wouldn't let anyone else have them. They were possessions to him."
As Josh tangled with Susan's relatives over the boys, Charlie, 7, and Branden, 5, Cox says he relayed his concerns to his attorney, to the court, to the county sheriff, to family services officials.
"They were all aware of our fears – that he would take a cowardly way out," says Cox.
Powell, who had denied wrongdoing
in his wife's disappearance, had been fighting to regain custody
of their boys, who were being cared for by their maternal grandparents.
A judge had recently ordered Powell, whose father is the subject of a child pornography case
, to undergo a psychosexual evaluation, according to reports.