New Clues Emerge on Day of Powell Childrens' Funeral As the Cox and Powell families prepare to lay Charlie and Braden Powell to rest this morning, police are closing in on new clues that they hope will help them find out what happened to the slain boys' missing mother. Charlie and Braden were killed last Sunday when their father Josh Powell attacked them with an axe during a supervised visit before igniting an explosion in his home. Josh Powell also died in the blast. Today's memorial service will take place at the Life Center in Tacoma, Wash. On Friday, authorities discovered a blood-stained comforter in Josh Powell's storage unit, however it remains unknown whether the blood is from his missing wife, Susan, who disappeared on Dec. 7, 2009. Josh Powellvisited the unit one day before he killed himself and his two sons, Charlie, 7, and Braden, 5. Police also released surveillance footage of Powell withdrawing $7,000 dollars from a local bank. And in a new twist, police are now closing in on Josh Powell's father, Steven, calling him a "person of interest" in Susan Powell's disappearance. Steven Powell is in jail on unrelated charges of voyeurism and child pornography. Powell has denied the charges. In an interview with ABC News last year, Steven Powell claimed he shared a sexual relationship with his daughter-in-law. "There's no question in my mind that the feelings were mutual," he said. Powell's sister, Alina, portrayed her brother as a victim and said she believes he did not kill his wife. Powell, who was reportedly upset he had been denied custody of his two sons, slammed the door on social worker Elizabeth Griffin-Hall when she brought Charlie and Braden, for a biweekly supervised visit with their father. "I'm saying, 'Let me in, Josh, let me in,'" Griffin-Hall told ABC News in an exclusive interview. Josh Powell's lawyer, Jeffrey Bassett, said he received an email from him minutes before the explosion that said "I'm sorry, goodbye." Bassett didn't see the email until two hours after the blast. At a hearing the week before, Powell was ordered to undergo a psychosexual evaluation and polygraph test in order to get his children back after it was revealed police had found realistic computer-generated depictions of parent-child sex on his computer, Detective Ed Troyer of the Pierce County Sheriff's Department told the Associated Press. Charlie and Braden Powell were to remain with their maternal grandparents, Chuck and Judy Cox, until their father's next hearing, which was scheduled for July. ABC News' Colleen Curry contributed to this report