SPOKANE VALLEY, Wash. -

A Spokane Valley woman helped her boyfriend try to dispose of her mom's body after he allegedly killed her and then went on an Internet shopping spree while draining her mom's bank account, according to court documents.

Those documents outline the role Rachael Colby, 29, allegedly had in the death and subsequent cover-up of the death of her mother, LaTanya Chapin, whose body was found in the trunk of a car at the Richard Allen Court Apartments last week.

Colby, who is currently in custody at the Spokane County Jail, was charged Monday with second degree murder for her mom's killing. Previously she was charged with a count of rendering criminal assistance by hiding evidence in her mom's murder and then helping dispose of her mom's body, as well as a charge of trafficking stolen property by selling items purchased using her deceased mother's bank account.

Detectives started to unravel the mystery behind Chapin's disappearance -- and her daughter's suspected role in her killing -- after a call from Chapin's sister, who confirmed she had not been seen since February 24. The sister said she feared that her sister's daughter, Rachael Colby, and her boyfriend had harmed LaTanya.

They also spoke with the father of one of Chapin's children, who confirmed LaTanya was scared of the people her daughter was spending time with, and asked him if it was alright if she and one of her other daughters moved in with him down in Tri-Cities. He agreed to let her move in, but the last time he heard from her was February 24.

Third hand information led detectives to an individual who had been contacted by Colby and her boyfriend, Edward Juan Sifuentez, to see if he would help them dispose of a body. The man went with Colby and Sifuentez to the residence they had shared with Chapin and noticed bloody blankets and a large amount of blood on the floor of the garage. He backed out, saying he didn't want to have anything to do with the situation, but detectives said Colby and Sifuentez returned to his home the next day in a Ford Probe and told him the body was in the trunk of the car. They tried to solicit the man's help to dump the body but he refused to assist them.

Based on the information this witness gave detectives, Spokane Police were called to help locate the Ford Probe, which they subsequently found. A detective went up to the vehicle and spotted a hand sticking out into the passenger compartment of the vehicle from the trunk / hatchback area of the car, so the vehicle was impounded and the body later removed.

The next day Colby was called in for questioning and court documents outline her statement to detectives that Sifuentez had killed her mom using a baseball bat and then later asked for her help to get rid of the body. She told detectives she helped load her mom's body into the trunk of the car, drove the car to the witness' house and later drove the car to the spot where they left it.

Colby confessed that after her mom was dead she and her boyfriend accessed her mom's bank accounts, ordering items online, such as cell phones which they then in turn sold at a kiosk in the Spokane Valley Mall for cash.

She admitted Sifuentez had never threatened her until two weeks before she was called in to be interviewed by detectives last week, but even still she had quietly defied her boyfriend's orders to dispose of the alleged murder weapon.

Sifuentez, according to Colby, had told her to take the bat and get rid of it. Instead of disposing of it, Colby took the bat to a storage unit in Spokane Valley and hid it from him. Spokane County Sheriff's detectives executed a search warrant at that storage unit last week.

On Monday, Sifuentez made a court appearance on his murder charge and his bond was set at $750,000. Velia Duenas, his mother, said her son didn't kill Chapin.

"I believe him, that mother instinct, I didn't feel like he was lying to me because he looked at me in the face," she said.

Colby has not made a first appearance on the new murder count she was charged with Monday.