Megan Huntsman, 39, was heavily into a meth addiction when she strangled or suffocated the infants from 1996 to 2006, Pleasant Grove Police Capt. Mike Roberts told The Associated Press. She wasn't worried about potential health problems caused by her drug abuse while pregnant, she simply didn't want to care for them, he said.
"It was completely selfish. She was high on drugs and didn't want the babies, or the responsibility," Roberts said. "That was her priority at the time."
Authorities think a seventh baby found in her Pleasant Grover garage was stillborn.
Police had previously declined to discuss a motive, which they say was uncovered during interviews with Huntsman.
Huntsman is in jail on $6 million bail, charged with six counts of first-degree murder. She is due back in court in Provo on July 21 and has not yet entered a plea.
Her lawyer, public defender Anthony Howell, declined comment Tuesday. He said office policy precludes him from discussing open cases.
Huntsman's estranged husband, Darren West, spent more than eight years in federal prison after pleading guilty to possessing chemicals intended to be used in manufacturing methamphetamine. West was released from a federal prison in California in January and transferred to a halfway house in Salt Lake City.
West was the one who made the grisly discovery on April 12 while cleaning out the garage of the home he had shared with Huntsman. He told police he found the baby in a small white box covered with electrician's tape.
The six other bodies were found after police obtained a search warrant for the home. Documents show they were all found wrapped in shirts or towels inside individual boxes in the garage.
Officials were doing a psychological examination of Huntsman in jail, the results of which have not yet been revealed.
Police also announced Tuesday that DNA results revealed that five of the babies were girls and two were boys. All seven were full term, Roberts said.
Those tests also confirmed that West was biological father of the seven infants. He lived with Huntsman during the decade their children were killed before going to federal prison on the drug charges from 2006 until January.
Investigators are still trying to pin down how West didn't know about the pregnancies or deaths, but Roberts said he is not a suspect in the case. They don't plan to bring him in again for questioning.
Huntsman remains the only suspect in the investigation, which remains open, Roberts said. Detectives are waiting to get results back from criminal forensic testing that Roberts declined to elaborate on.
Previous tests from the Utah state lab found that the babies were likely dead anywhere from two to 10 years or more, Roberts said.
The day of the grisly discovery, Huntsman told police that were eight or nine dead babies in her home, a previously released search warrant affidavit showed. But Roberts said Huntsman was confused and was taking a ballpark guess.
Roberts said Tuesday investigators continue to believe there were only seven.
The FBI was brought in to help with the investigation because no labs in Utah could analyze the type of DNA taken from the small corpses.