FORT WORTH, Texas -- Police in Texas say Stephen Barbee admitted to having an affair with Lisa Underwood and getting her pregnant, and to killing the woman and her young son to cover it up.

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Video: Police Find Bodies Of Pregnant Woman, Son | Earlier Police News Conference
Slideshow: Lisa And Jayden Underwood
Extra Info: Case Timeline
Web Site: www.findlisaandjayden.com

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Police said Barbee admitted to beating and strangling Underwood, 34, and her 7-year-old son, Jayden, in their home Friday night after Underwood threatened to tell Barbee's wife about the affair.

Police arrested Barbee, 37, of Fort Worth Monday night in Tyler and charged him with two counts of capital murder in connection with the deaths.

On Tuesday, police said they located two bodies they believed were the pregnant north Fort Worth woman and her 7-year-old son after Barbee led them to the scene not far from the Texas Motor Speedway near Northlake, about 25 miles north of Fort Worth.

Police said in a press conference Tuesday afternoon that identifications were not confirmed, but said they know a shallow grave at the site contains the bodies of a female and male consistent with the ages of Underwood and her son.

Barbee was arraigned in Tyler Tuesday morning, and was being transported to Fort Worth where he would be held on a $2 million bond, police spokesman Lt. Gene Jones said in a press conference Tuesday morning.

Authorities canceled a nationwide Amber Alert for Underwood and her child Tuesday morning.

Police have been in contact with Jayden's father, who lives in another state, Jones said.

Police, acting on an anonymous tip, searched a north Fort Worth home overnight. Fort Worth police said they found a specific item they were directed to, but they haven't said what that item is or how it figures into their investigation.

"It is a major step forward. Of course, it doesn't solve the case, and so, our efforts are still very aggressive and we're going to ensure that we conduct the most thorough investigation possible," Jones said Monday.

Investigators removed a roll of carpet from the Underwood's home.

Underwood's SUV was found Tuesday, nose down in a creek near Denton, north of Fort Worth. Police called that a major step forward in the investigation. Authorities canceled a nationwide Amber Alert for the woman and boy Tuesday morning

Police said the keys were found in the unoccupied vehicle, but would not release any further details.

Police used bloodhounds Monday to search the area of South Hickory Creek near Denton Municipal Airport, where the SUV was discovered.

Investigators believe Underwood and the child were abducted from their home in north Fort Worth.

Friday night was the last time anyone had heard from the woman. Underwood and Jayden not only missed a morning birthday party, but Underwood also missed her own baby shower.

Outside the Underwood home, someone wrote a chalk message on the concrete, wishing the mother and son a quick return. Friends plan a candlelight vigil Tuesday night.