Unsealed court documents regarding Josh Powell have convinced Denise Cox, the sister of Susan Powell, that police could have prevented the deaths of her two nephews.  

In 2009, Susan Powell went missing. Her husband, Josh Powell, told authorities that he took their sons on a camping trip. Her family believes she is dead, but her body was never found, reported the Daily News. Police from West Valley City, Utah, investigated Josh Powell as the lead suspect. However, after nearly three years, they were unable to make an arrest or find the body of Susan Powel. Josh Powell moved to Washington state with his two children.

In February, Powell murdered his two boys and took his own life by igniting a house into flames.

Court documents unsealed by Pierce County, Wash., Friday reveal that Utah police had accumulate more evidence in connection with Josh Powell's involvement with his wife's possible murder and disappearance than previously known, reported ABC.

Cox, however, blames the police for not acting on the information. She said that if they had, her nephews would be alive today.

Look what it did -- it killed my nephews, by not putting [Josh Powell] behind bars when he should have been, Cox told ABC News. They didn't act on anything that they should've acted on.

The documents reveal that police found Susan's blood on the tile floor next to the carpet adjacent to the sofa, in the couple's home, reported ABC. When police searched the home after Susan's disappearance they discovered two fans were set up and blowing onto the couch and that it appeared to have just been cleaned.

Police also discovered a letter inside Susan's safety deposit box that discussed her impending death. The letter was reportedly stapled around the edges addressed to her family and friends specifically asking that it not be shown or given to her husband Joshua Powell, writing that she did not trust him, said the court documents. The letter said that if she was killed, it may not be an accident, even if it looks like one.

Cox said that police could have used this evidence to keep her nephews from seeing Josh Powell. And she believes her and her family should have been told about the letter.

They were foolish in keeping it from us, Cox said. All the signs were there and the police didn't act on it.

Susan's father, Chuck Cox, also attacked the police department for not acting on the possible evidence.

The children would be safe, he said, according to the Deseret News. How much more do you need? It's just very frustrating.

However, the mayor of West Valley defended the police department.

It is easy to Monday morning quarterback these things. It is easy for those of us who watch TV to say, 'Hey, there is plenty of evidence,' said Mayor Mike Winder, according to the Deseret News. It is a different matter if you are in the legal community to have enough evidence to go in for an arrest.