Rosa Hill admitted Monday that she killed her husband's 91-year-old grandmother but claimed that she did so in self-defense and because she was distraught about a custody battle over the couple's daughter.
Hill, 36, told a jury in Oakland that she went to Selma Hill's home in the 7700 block of Peppertree Road in Dublin on Jan. 7, 2009, because her then-husband, Eric Hill, lived there with their daughter and she believed that he had been molesting the girl, who was 2 years old at the time.
Eric Hill has denied that he molested his daughter.
Rosa Hill said that when she climbed a tree early that morning and peeked into a bedroom window, she saw her husband and daughter both naked.
"I wanted to stop him but I wasn't sure what to do," she said.
Hill said her husband, from whom she was later divorced, had sole legal custody and 85% physical custody of their daughter, and she was afraid to call police unless she had strong proof that he was molesting the girl.
Hill said she eventually climbed down from the tree and rang the doorbell, but no one responded.
She said that after her husband drove off, apparently to go to work, she heard Selma Hill taking out the garbage and tried to talk to her about her concern that Eric Hill was molesting their daughter.
But Rosa Hill said Selma Hill told her that her grandson "could do whatever he wanted to do" because he had custody and "if I interfered I would never see my baby again."
Rosa Hill said she was "shocked" and "really upset and angry" about Selma Hill's comments.
She said Selma Hill "picked up a knife" and "it seemed like she was swinging the knife toward me."
She said that in response, she picked up a broom and "just started hitting (Selma Hill)."
"I just started seeing red and I couldn't see anymore," she said.
"At some point I hit her hard and knocked the knife out of her hand and she reached over to grab something else," Hill said.
Hill said she "completely lost it."
"At some point I think I Tased her and I think I shoved her back really hard with the broom and she started falling," Hill said.
Hill said Selma Hill started gagging and lost consciousness. She said she didn't know whether the elder woman was dead so she used a stun gun on the 91-year-old "to see if she moved."
"I know it doesn't make sense but at the time it was all I could think of," she said.
She said she finally realized that Selma Hill was dead "after I used the stun gun on her a few times and she didn't move."
Hill said she didn't call police because she didn't know how to handle the situation and was concerned about what would happen with her daughter.
Hill and her mother, 57-year-old Mei Li of Antioch, are both charged with murder for Selma Hill's death, and with attempted murder for allegedly attacking Eric Hill later that day after he returned to his grandmother's home.
Prosecutors contend Li was there for the attack on Selma Hill, but Li's attorney claims she only arrived at the home later, after her daughter called and asked for her help.
Prosecutor Casey Bates told jurors in his opening statement last month that Rosa Hill and Li planned the attack at Selma Hill's home for months, buying a gun, stun guns, a hammer, a sword, a crossbow, an axe, a hacksaw, handcuffs, pepper spray and other weapons.
He said they also did extensive research on the Internet on how to get away with murder and use deadly substances such as arsenic, nerve gas, mustard gas and ammonia.
But Rosa Hill's lawyer, Bonnie Narby, told jurors that she does not think the alleged attack was a murder because Hill never intended to kill Eric Hill or his grandmother.
Instead, Narby said she thinks Rosa Hill acted in the heat of passion because she was overwhelmed by the custody battle over the couple's daughter and their divorce proceedings.
Rosa Hill faces a term of 44 years to life in state prison if she's convicted of all the charges against her, and Li faces 38 years to life.
Ping Li, 70, the husband of Mei Li and the father of Rosa Hill, is charged with being an accessory in the case but will be prosecuted separately at a later date.