A missing pregnant woman's mother said the whole family has been deceived by her son-in-law, a "person of interest" who has been hospitalized.

Police discovered that Mark Hacking (search), 28, had lied about graduating from college and getting into medical school, authorities said Thursday.

Hacking has not appeared publicly since Monday, when he said his 27-year-old wife, Lori, never returned from a morning jog. The disappearance came days before the couple were to move to North Carolina, supposedly so that he could attend medical school.

Hacking entered the University Neuropsychiatric Institute Monday night after being questioned by investigators, FOX News has learned.

He checked himself in because of stress, according to his brother, Lance. Detective Dwayne Baird confirmed that Hacking was hospitalized but would not give details.

Hacking's family and in-laws said they were stunned to learn on Wednesday that he had not graduated from college or been accepted at a medical school, as he had claimed.

Thelma Soares, Lori Hacking's (search) mother, said that she was certain her daughter had not known about the discrepancies. "Up to the time when I spoke with her last, she was deceived also," she told KUTV-TV.

Soares, addressing herself to her son-in-law, said: "We feel badly that you felt that it was necessary to perpetuate this deception. We love you, no matter what."

Police Chief Rick Dinse said "there is no question (Mark Hacking) is a person of interest" in the disappearance of his wife, but said he would have been regardless of the lies he told about his education.

Authorities want to know why he bought a new mattress on Monday, the day Lori disappeared.

Police took the couple's box spring mattress from their apartment and a Dumpster was hauled away to a forensics lab. There was no word on what happened to the old mattress.

Douglas Hacking said he spoke to his son at the hospital about the deception.

"He has two older brothers who are high achievers, a physician and the other is an electrical engineer," the elder Hacking said. "He felt under some pressure to excel as well. It has finally come to an end, and he's relieved."

The University of North Carolina (search) said Wednesday that Hacking had never applied to the medical school. Also, the University of Utah (search) said he was enrolled from 1999 to 2002, majoring in psychology, but never graduated.

More than 1,200 volunteers scoured the steep terrain surrounding a park and canyon in a search for Lori Hacking on Tuesday, and on Wednesday, volunteers took fliers door-to-door in downtown Salt Lake City neighborhoods.

Friends said the couple learned last Thursday that Lori was five weeks pregnant, although The Salt Lake Tribune on Wednesday quoted police as saying that had not been confirmed. Lance Hacking said Thursday that Lori showed the positive at-home pregnancy to her sister-in-law.

Fox News' Carol McKinley and The Associated Press contributed to this report.