The sister of Joshua Powell will offer criticism of her brother on Tuesday's episode of "Dr. Phil," according to a preview of the daytime talk show released Saturday.

Utahn Jennifer Graves will discuss the case of her missing sister-in-law, Susan Powell. Graves' brother, Joshua Powell, 34, is the only person of interest publicly named by West Valley City police in connection with Susan Powell's disappearance.

He has provided little information to police or family members -- a point of frustration for Graves. "I'm kind of caught in the middle. My brother is a person of interest, but my sister-in-law, my good friend is missing," said Graves, in the episode taped last week.

"What has bothered me the most [is that] he has been reluctant to participate in the media arena. That's our biggest tool in helping to find Susan. You are the husband! There is more that you can do! So get up and do it!"

Graves also said her brother avoids questions about his wife's disappearance.

"I asked him if he was involved and he wouldn't respond ... he literally doesn't say anything ... [he said] 'My lawyer said not to talk to anyone,'" his sister said during the show.

In addition to Graves, Susan Powell's parents, Chuck and Judy Cox; Shelby Gifford, a family friend who has served as a spokeswoman during the search for Susan; and Graves' husband Kirk will appear on the program to talk about the search.

Susan Powell, 28, was reported missing Dec. 7.

The program airs on KUTV Channel 2 at 3 p.m. and KJZZ Channel 14 at 8 p.m. Tuesday.

Phil McGraw hosts the one-hour show, which is the second highest-rated daytime talk show in the nation, according to www.drphil.com.

In the preview, Chuck Cox is said to discuss how he tried to be supportive of his son-in-law, but has since cast doubt on Joshua Powell's story of camping past midnight in subfreezing temperatures.

"In the beginning I wanted to be supportive, I believed that there would be a reasonable explanation ... but as my son-in-law shut down [it became] really hard to keep positive," Cox said, according to the preview.

"It's frustrating, he won't cooperate with the police and that's impeding the investigation and it's stopping us from finding my daughter."

Police have said Joshua Powell told them he took their two sons, now ages 3 and 5, camping at 12:30 a.m. the day Susan disappeared, leaving his wife at the family's West Valley City home. Joshua Powell, has since moved to his hometown of Puyallup, Wash., with the boys. He recently returned to Utah to fix up his home to rent to neighbors.

Also appearing on Tuesday's "Dr. Phil" will be Ed Smart, father of kidnapping survivor Elizabeth Smart. Smart has offered support to Chuck and Judy Cox throughout the search. He said on "Dr. Phil" he was forced to endure intense police questioning about his daughter's disappearance, but he did as much as possible to cooperate.

"To us it was all about finding Elizabeth and it didn't matter what the police wanted, we wanted to do whatever it would take to find her because nothing was more important to us. That just doesn't seem to be the case with Josh," Smart said, according to the preview.

mrogers@sltrib.com