She watched the two children starve to death but claims she was too scared to do anything about it.
Reina Gonzales, now 24, says she urged Christopher Payne to send his kids back to their mother, Jamie Hallam, who testified earlier in his trial.
According to her testimony, Payne refused, saying Hallam, clean now for a little over than two years, was using methamphetamine.
Gonzales said Hallam dropped the two children, Tyler and Ariana, off at the couple's apartment for a weekend visit.
Under a divorce settlement, Hallam had custody of the children, and Payne had no visitation rights, but she let them have the kids for a weekend anyway.
Gonzales testifies Hallam kept asking to get the kids back, but Payne refused and lied to his ex-wife, saying the kids were staying with an aunt or with friends every time their mother demanded the children.
Eventually, as the couple used heroin and lost their jobs, the two children were locked in a closet, living on a peanut butter and jelly sandwich a day, and they eventually starved to death.
Meanwhile, Payne and Gonzales were raising a third child, Christopher Jr., whom Gonzales says was treated well.
"Did you see the children's bodies?" Prosecutor Susan Eazer asked Gonzales.
"Yes," she replied.
"What did they look like?"
"I could see nothing but their bones," answered Gonzales.