SAN DIEGO -- A mother of six accused of smothering her newborn son while staying with relatives in Rancho Penasquitos pleaded not guilty Friday to charges of murder and assault on a child under 8 causing death.

Julie Alison Reynolds, 36, faces 25 years to life in state prison if convicted, said Deputy District Attorney Tracy Prior.

"This defendant smothered her newborn baby boy, placed him in a backpack, and hid him in a closet," Prior said outside court. "This baby died of no other medical reason (than) but for at the hands of another."

Prior said Reynolds placed her left hand over the newborn's nose and mouth, killing him. The child's body was found Wednesday in the defendant's bedroom closet.

The prosecutor said Reynolds had six children by three different men, ranging in age from 18 months to 17 years old, and the victim would have been the defendant's seventh child by a fourth man.

Prior said Reynolds has a documented history with Child Protective Services in two states other than California.

The prosecutor said Reynolds' sister and brother-in-law had welcomed the Colorado woman into their home a few months ago in order to help her get her life on track.

The couple didn't know Reynolds was pregnant, but noticed some weight gain and repeatedly asked the defendant if she was with child, but she denied it, Prior said.

Last weekend, the couple became extremely suspicious when they noticed Reynolds' weight loss and found blood on the carpet in the defendant's bedroom, Prior said.

"They inquired, 'Did you deliver a baby? Did you deliver a baby? She denied,'" the prosecutor said.

The brother-in-law went through the trash and found a plastic bag with bloody towels, then went to the police for help, the prosecutor said.

When officers arrived, they found the 6-pound, 19-inch baby dead in the backpack, Prior said.

Officers took Reynolds to downtown SDPD headquarters for questioning, when she allegedly made statements implicating herself in the infant's death, police said.

The defendant's six children are in protective custody and the defendant's relatives have offered to take care of them, the prosecutor said.

Prior said the defendant knew she had the option of dropping the newborn off at a police or fire station, having her family help or giving the child up for adoption, but chose none of those options.

Superior Court Judge David Szumowski ordered Reynolds held on $1 million bail and scheduled a status conference for Thursday.