Steven Powell, the father-in-law of missing Utah woman Susan Powell, appears in Pierce County courtroom, Sept. 23, 2011, in Tacoma, Wash. (Ted S. Warren/AP Photo)

Josh Powell's father has filed paperwork stating that he will not answer any questions from law enforcement authorities about the disappearance of his daughter-in-law, Susan Cox Powell.

Steven Powell submitted a notice to law enforcement in Pierce County Superior Court invoking his Fifth Amendment right to not answer questions posed to him by authorities about the case. The filing comes two weeks after his son, Josh, blew up himself and his two children, Charlie and Braden, in a rental home. In the wake of the deaths, police said they would ask Steven about Susan's disappearance in 2009.

Steven had previously been outspoken about his daughter-in-law's disappearance, making statements to the media about how Susan likely ran away from her family to be with another man.

But now he will not answer questions by any police, including the West Valley City, Utah, police department, which investigated the disappearance, and the Pierce County Sheriff's department, which arrested Steven in September on child porn and voyeurism charges.

He was arrested following a search of the home he shared with Josh and the children in September, which was conducted as part of the investigation into Susan's disappearance. His trial on child pornography charges is set to start March 20.

Josh was long considered a "person of interest" in the case of his missing wife. Now, with Josh dead, police have called Steven a "person of interest."

Steven's lawyer did not return calls for comment.

The news  comes just a day after authorities in Pierce County, Wash., said that Josh Powell was still living at his father's home right up until his death, and only rented a small home nearby to convince authorities that was where he was living so he could regain custody of his children.

Detective Gary Sanders said that Powell wasn't really living in the rental home at all, and was spending the majority of his time at Steven Powell's home in Puyallup, where police had previously found thousands of images of child pornography and graphic decorations.

Neighbors at the rented home told police they never saw Powell there, while neighbors of Steven's home said Josh Powell was there all the time. Police also said the home was decorated with pictures of the boys' missing mother.

Police said that if state authorities knew Josh Powell was still living in his father's home where child porn was found, he would not have had a chance at getting custody of his children again. In addition to the sexually explicit images found in the home, police also found a noose and a poster of a naked woman with a sword through her body, along with other items that have not been publicly disclosed. The list of items found during the search is sealed until Steven Powell's trial, they noted.

Following Steven Powell's arrest, the two young boys were taken out of Josh Powell's custody because of the material found in the home. They were placed with their maternal grandparents, Chuck and Judy Cox.

Josh Powell's motion to regain custody was denied just four days before he killed the children and himself.