The family of Josh Powell is asking a judge to declare that Susan Powell was dead before May of last year.

Terrica and Alina Powell — Josh Powell's mother and sister, respectively — filed a complaint Friday in 3rd District Court against Chuck Cox, Susan Powell's father and conservator of her estate.

In that complaint, the Powells argue that Cox amended the trust in May 2013, and listed himself as the sole beneficiary of the trust that Josh and Susan Powell set up in February 2009.

The Powell's attorney, Joshua Lee, said in a prepared statement Friday that Cox should not have been able to amend the trust, and it should have become irrevocable upon Susan Powell's death — which he said likely occurred before May 2013.

In the original trust, Josh and Susan Powell had agreed that their assets and life insurance awards would be split evenly between their two families, Lee said in the court complaint.

"It should be emphasized that, like the Cox family, Terrica and Alina are also victims of the tragic events surrounding the Josh and Susan Powell family," Lee said in the prepared statement. "[They] seek only to protect the integrity of their legal rights and restore the trust's original intent, as established by Josh and Susan themselves."

Terrica and Alina Powell are asking that a judge declare that Susan Powell's death occurred before May 2013, and that Cox's amendment to the trust is void.

In September, 3rd District Judge L.A. Dever prevented Josh Powell's family from collecting any more money on his estate, saying they waited too long to challenge changes to his legal trust. The ruling will prevent the Powells from collecting assets in Josh and Susan Powell's trust when Susan is declared dead, which will likely be in December — five years after her disappearance.

Susan Powell, 28, was last seen Dec. 6, 2009, at her West Valley City home. Her husband Josh was the only person of interest when he killed their two sons and then himself Feb. 5, 2012, at a home in Graham, Wash.

Utah law allows for a person to be declared dead five years after anyone last saw signs of them.

While Dever ruled in favor of Chuck and Judy Cox, he did find problems with how they came to manage their daughter's estate.

Dever said Chuck Cox should not have been put in charge of the estate. The terms of Josh and Susan Powell's legal trust said a trustee could be appointed only if they were dead or incapacitated.

While Josh Powell is dead, Susan Powell has never been found, and Chuck Cox did not provide documentation from two doctors saying his daughter was incapacitated, as required by the terms of the trust. Once he gained stewardship of the trust, Dever said, Chuck Cox did not have authority to remove the Powell family as beneficiaries.

Yet, 3rd District Judge Katherine Bernards-Goodman granted Chuck Cox conservatorship over the trust on Jan. 30, 2013. Utah law provided the Powell family 30 days to challenge his appointment.

The Powells did not file any such challenge until Sept. 13.

Despite missteps by the Coxes, Dever let stand their booting of the Powells.

jmiller@sltrib.com

Twitter: @jm_miller