Utah police vow to continue probe into Susan Powell's disappearance Police in Utah said Monday that the death of Josh Powell -- the only person of interest in the disappearance of his wife, Susan, near Salt Lake City in 2009 -- will not necessarily hinder their ongoing efforts to solve the perplexing case. "We've been making progress with the investigation from the very beginning, and it still continues to progress," West Valley City Police Sgt. Mike Powell told the Los Angeles Times. Powell, who died with his two sons Sunday in Washington state after apparently torching his house during a supervised visitation, had not been cooperating anyway, said the sergeant, who is not related to the Powell family. "We have stated in the past that Josh Powell has been a person of interest, and I don't think there's any problem with repeating again that he has not been cooperative with our investigation, so it doesn't necessarily change a whole lot on our end," he said. The West Valley City Police Department has sent a team of investigators to Graham, Wash., to coordinate with police there and determine if there are any additional leads to be gleaned at the scene of Sunday's fire. Police said a state contract social worker was dropping off the Powells' two sons, ages 5 and 7, for a supervised visit when Josh Powell suddenly blocked her entrance and locked the door. Moments later, an explosive conflagration broke out, quickly consuming the house and killing all three people inside. Autopsies on the victims were scheduled for Monday. Steve Downing, an attorney for Charles and Judith Cox, Susan Powell's parents, told the Associated Press that the boys had begun talking about the snowy night in 2009 when Josh Powell loaded them into the family vehicle for a midnight camping trip. They said their mother was "in the trunk," and then disappeared after that, Downing said. Josh Powell sent an email to his lawyer only minutes before the fire, saying: "I'm sorry, goodbye," the AP reported. Powell's brother-in-law, Kirk Graves, said he believes Josh may have worried that his sons were divulging information about the night of his wife's disappearance that he didn't want known. "I imagine that part of Josh's motivation was what could he do to hide that story, to avoid having to deal with the consequences of what he had done," Graves said in an interview with NBC's "Today" show. He said he was convinced that Powell "really only cared about himself," and was seeking to cause pain to others in the family, who had successfully prevented him only last week from regaining custody of his sons. "He just took an opportunity to hurt everybody around him, and he used the boys as a tool to do that," Graves said. Police said they would release no additional details as the investigation progresses. "The West Valley City Police Department is deeply saddened by this tragic event and extends their deepest condolences to all those impacted by this loss," the department said in a statement.