A trial in a lawsuit against Washington state began Tuesday.
Josh Powell was suspected in the 2009 disappearance of wife Susan Cox Powell when he killed his sons in 2012.
Susan Powell's parents have sued the state Department of Social and Health Services, alleging negligence helped contribute to their grandsons' deaths. A caseworker had brought the children to their father's home for a supervised visit, but he locked her out, attacked the boys, poured gasoline on them, and killed them and himself in an explosive fire.
"How could the state have allowed this visitation at the one place on earth that Josh Powell had complete control?" said Cox family attorney Ted Buck during opening statements.
Buck graphically described how Powell killed his sons and told jurors the family is asking for $5 million for every minute the boys suffered. Buck told jurors the boys died from carbon monoxide poisoning up to 10 minutes after being injured by their father.
Powell attacked his boys with an ax before pouring gasoline around the house and setting it on fire.
Buck said the state should have recognized that Powell was a risk to the boys.
"Anybody associated with the case should have seen that coming, and yet the state did nothing," Buck told jurors.
The state's attorney, Assistant Attorney General Lori Nicolavo, argued the only person who should be blamed for the murders is Powell.
Nicolavo noted Powell had not been charged with any crime and the boys showed no signs of abuse preventing the state from taking further protective action.
She also told jurors investigators in Utah did not share evidence they had about Powell with Washington investigators.
Before the murders the state supervised more than 20 visits between Powell and his boys without incident.
"He was doing everything that was asked of him, maybe putting on a good show, but taking every step that he needed to take to get his boys back," said Nicolavo.
The trial is expected to last a month, said a spokesperson for the Cox family.