It's the most specific Josh Powell and his father, Steve Powell, have been in theorizing what might have happened to Susan.
On the website run by the Powells, Josh and Steve make their case: Susan Powell and Koecher are about the same age, members of the LDS Church and both were in West Valley City during the week of their disappearances in December 2009. The website alleges that Susan Powell and Koecher absconded to Brazil, where they potentially married and started a new life.
Family members of both Susan Powell and Koecher say there is no truth to the story.
The website claims Susan Powell was leading a "secret double life" and that her family had been "attempting to destroy" her marriage.
The website also says Susan was emotionally abused by her family and that her mother suffered from mental illness, which came on later in life.
"Susan was very concerned that she was beginning to experience similar effects as her mother, Judy Cox," the website states.
It goes on to say that Susan Powell had struggled with emotional issues and anger management, but had worked hard to improve. However, Josh Powell felt like those issues began to worsen in 2009, and he encouraged her to see a psychiatrist, saying she was becoming her mother.
"Josh now realizes that this was the last thing she needed to hear," the website states. "Josh used the wrong approach, thus bringing one of her worst fears to life, and he deeply regrets it."
Shelby Gifford, spokeswoman for Susan Powell's parents, Chuck and Judy Cox, says there is no history of mental illness in the Cox family and that no one but Josh has ever said Susan Powell suffered from any kind of emotional instability.
The website has a link to a nine-page letter, prepared by Steve Powell for federal law enforcement agents, claiming that Susan Powell and Koecher absconded to Brazil together. Steve Powell points to Koecher's LDS mission to Brazil and Susan Powell's interest in learning Portuguese and her "casual belief" in the LDS Church that would allow her to have an extramarital affair despite the LDS Church's belief that is a sin.
The letter also says that Susan Powell easily would have been able to leave because of her husband's sometimes odd behavior.
"Josh created the perfect disappearance-by-husband scenario for her by just being Josh," the letter states.
The website also details parallel timelines, personalities and work histories for Susan Powell and Koecher.
Steve Powell suggests to authorities to look at marriage records in Brazil as both Susan Powell and Koecher would have access to LDS temples in which to marry.
"I am about 100 percent certain that Koecher absconded, and about 75 percent certain that Susan did likewise. I am about 75 percent certain that if one is found the other will be with them," Steve Powell writes. "I am not nearly that certain that they went to Brazil. However I can't think of a more fitting place for a couple with their background to disappear without a trace."
Deanne Koecher, mother of Steve Koecher, says she welcomes any attention brought to her son's missing person case, but she sees no connection between the two disappearances.
"The parallels don't hold water for us at all," she said.
Her son, 30 years old at the time of his disappearance, did have a passport, but it was found among his belongings and had not been used to leave the country, she said. The West Valley Police Department contacted the St. George Police Department to find any links between the cases, but came up with none, she said.
The Koechers last knew their son to have been in Henderson, Nev., where a security camera captured an image of him on Dec. 13, 2009, walking down the street. Police found his car abandoned in the city a few days later.
Susan Cox Powell, 28 at the time of her disappearance, has been missing since Dec. 7, 2009.
Cox family spokeswoman Gifford says even if Susan Powell had run off with another man in a moment of weakness, the idea of her leaving her boys behind is "ridiculous."
"None of us have a problem imagining she would leave Josh, but we all know she would have not left her children," Gifford said.
The fact that both Utahns disappeared in the same week made the Cox family question whether a connection existed between the disappearances, but Gifford said after talking with authorities, they concluded there was no connection.
"It's a shame the poor Koecher family needs to be put through such misery," she said.
On the Web
To read the letter from Steve Powell, visit www.susanpowell.org and click on the "Parallel Disappearance" link.