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Ted S. Warren, Associated Press
Don Easton, a special investigator with Unified Investigations & Sciences, Inc., collects evidence, Tuesday, Feb. 7, 2012, in the charred rubble of the home where Josh Powell and his two sons were killed Sunday, in Graham, Wash., in what police said appeared to be a deliberately set fire. Powell, the husband of missing Utah woman Susan Powell, died along with his children Sunday in Washington. An autopsy showed the children also suffered hatchet wounds to their necks. He was a person of interest in his wife's 2009 disappearance.

OLYMPIA, Wash. — Utah authorities have for at least six months investigated the disappearance of Susan Powell as a murder case. But without a body, they publicly held out hope that she would be found alive.

So what evidence did they have that the mother of two was dead? And was there anything to identify her killer?

There was the damp spot on the floor in their Utah home and a curious late-night camping trip described by her husband. There were also the recollections of their young son Braden about a camping trip and his mother being "in the trunk."

That could strike some as a clue, or the ramblings of a boy who was then just 2.

For authorities in Utah, none of it was enough to bring charges.

The man identified by investigators as a "person of interest" — Powell's husband Josh — had already moved from Utah to Washington state, taking with him their two young sons. On Sunday, he torched his house, killing himself and the boys. A 911 call released by police late Tuesday revealed a social worker's frantic attempts to alert authorities that Josh Powell had locked himself and his two young sons in his home moments before he set the house on fire, killing everyone inside.

The social worker said she had just dropped off the boys and that a man grabbed them, and then wouldn't let her in the door.

Josh Powell was scheduled for a supervised visit with his sons. On the recording, the social worker tells a dispatcher she can hear one of the boys crying, then she screams, "He exploded the house!" after the fire began.

Now, as authorities try to determine what led him to take such a drastic measure, many questions remain about the status of the investigation into Susan Powell's 2009 disappearance and how close they were to bringing charges.

A Washington state search warrant obtained by The Associated Press through a public records request Tuesday showed that police were investigating three felonies in Utah: first-degree murder, kidnapping and obstructing a public servant.

Salt Lake County District Attorney Sim Gill acknowledged for the first time that investigators believe Powell is likely dead, but he said in an interview with the AP that the case remains a missing persons probe for now.

Gill wouldn't discuss the evidence but said authorities didn't have enough information to file charges.

"I think when I talk about it as a missing persons case, that's because we haven't located the body of Susan Powell," Gill said. "Do we think that she may have met harm? Sure. I think that's been an ongoing assumption with law enforcement."

Investigators said Josh Powell withdrew $7,000 in cash from a bank the day before he killed himself and his two young sons in the house fire.

Pierce County Prosecutor Mark Lindquist said detectives obtained Powell's bank records Monday, and on Tuesday they searched a storage unit he rented. It isn't clear what happened to the money.

Josh Powell claimed that on the night Susan Powell vanished, he took sons Charlie and Braden from their home in West Valley City, Utah, on a late-night camping trip. Authorities eventually searched the central Utah desert but found nothing.

Susan Powell's father said that when police went to the family home after she was reported missing, they found a wet spot in the house being dried by two fans. Police have not commented further on what they found.

When Utah authorities traveled to Washington following the blaze Sunday that killed 7-year-old Charlie and 5-year-old Braden, they didn't specifically address what the boys may have said.

West Valley, Utah, Police Chief Buzz Nielsen said authorities needed concrete evidence to move forward.

"When you charge on criminal cases, especially if it ends up being a homicide ... without a body, it's just more difficult. You have to have a stronger case to make those arguments in court," Nielsen said Monday.

"We have circumstantial evidence that I'm not allowed to talk about it," he said. "On a criminal case of this nature you've got one shot, beyond a reasonable doubt in court."

Last September, authorities got a warrant to search the home of Josh Powell's father, Steve. Josh Powell and his sons were living there at the time. The documents obtained by the AP did not specify a suspect.

In addition to the charges, the warrant listed Steve Powell's work laptop computer as well as cars that he used.

Authorities found explicit images on his computers during the search, and he was jailed on voyeurism and child porn charges. The boys were later sent to live with Susan Powell's parents.

Speaking to reporters Monday after the boys' deaths, their grandfather Charles Cox said the boys were emotionally distant when they first arrived at their home but recently had begun to open up.

That gave Charles Cox hope that someday they would be able say what happened to their mom.

The boys had not recently made more comments about what may have happened to their mother, Charles Cox said, though he related what Braden said nearly two years ago.

Cox said: "The four ladies that were supervising that activity said, 'Well, what's this?' 'That's us going camping.' 'Who's in the car?' And Braden said, 'That's Daddy, that's Charlie, that's me.' Then he said, 'Well, mommy's in the trunk.'

"Well if Mommy's in the trunk, why is she in the trunk?' He didn't know, he didn't say, I guess. Then, he said we stopped somewhere and mommy and daddy got out and mommy didn't come back," Cox said.

Nielsen said despite the death of the young boys and Josh Powell, the probe would continue.

"Our case is not closed," the police chief said.

Lindquist, who is overseeing the voyeurism prosecution of Steve Powell but is not directly involved in the Susan Powell case, said it's clear to him that it's a homicide case.

"I don't think at this point I'm going to call this a missing person case," he said. "It's reasonable to call Josh Powell's decision to kill himself and his kids a confession to the murder of Susan Powell."

Associated Press writers Brian Skoloff in Salt Lake City and Gene Johnson in Seattle contributed to this report.