CONCORD, Calif. (AP) _ Investigators believe the daughter of blues guitarist Elvin Bishop may have been involved in a botched extortion plot that led to her savage murder and the slayings of four others, including her mother.

Two brothers and their female roommate have been arrested on drug possession and burglary charges, and police consider them ``potential suspects'' in the slayings. The Contra Costa Times reported Friday that stains believed to be human blood were found in their home.

Investigators were conducting forensic tests to determine their origin of the blood.

Before her death, Selina Bishop, 22, may have joined the suspects in a plot to extort $100,000 from two other victims, an elderly couple, Concord police Lt. Paul Crain said Thursday.

``Why and when Selina became a victim is unclear,'' said Sgt. Douglas Pittman of the Marin County Sheriff's office.

The San Francisco Chronicle reported Friday that Bishop set up one or more bank accounts in the area for her boyfriend, Glenn Helzer, and deposited at least $25,000 of Helzer's money in them.

The newspaper, citing a lifelong friend of Bishop who was not identified, said that Helzer told Bishop in June that he was going to inherit between $100,000 and $125,000. The friend said he told Bishop he wanted the checks in her name so his wife wouldn't get any of the money.

Helzer, who was in the process of getting divorced, told her to open four or five accounts and told her she would get $5,000 of every $25,000 she deposited, the friend said.

Among the biggest mysteries are when and where Bishop was killed. Her remains and those of Ivan and Annette Stineman were believed to be spread among at least eight duffel bags pulled from a Sacramento County river this week. Bishop's mother, Jennifer Villarin, 45, and her friend Joseph Gamble, 54, were found Monday, shot to death in Bishop's apartment.

Investigators are also trying to determine whether the occult played a role in the slayings. Teeth and organs were missing from some of the victims, The San Francisco Chronicle reported Friday.

It's also unclear whether the Stinemans were forced to write two checks before they were killed or if someone forged the signature, Crain said.

Bishop _ or someone posing as her _ called a bank before the checks written to her name were cashed last week, Crain said. One police theory is that she was killed after objecting to the Stinemans' deaths.

A chain saw and a sawhorse were found inside the Stinemans' van, which was abandoned in Oakland with the keys still in the ignition, Crain said.

Bishop had been dating Helzer, 30, the elderly couple's former stockbroker, police said. Investigators said that connection helped them link the disappearance of the Stinemans and Bishop last week to the shooting deaths of Villarin and Gamble.

Helzer and his brother Justin Helzer, 28, were arrested Monday along with Dawn Godman, 26, in their Concord home. Police also found drugs.

The three were arraigned Wednesday but did not enter pleas. They were being held without bail and were due back in court Friday.

While no one has been charged in the murders, Glenn Helzer made statements linking himself to the elderly couple's disappearance, Contra Costa Deputy District Attorney Harold Jewett said.

The night Ivan Stineman, 85, and his wife, 78, were last seen alive, a neighbor saw two men with ponytails entering their home, Crain said.

Bishop was last seen alive with Glenn Helzer three days later at a Berkeley pub.

As police raided the Helzers' home, Godman and Glenn Helzer fled out the back door. Glenn Helzer allegedly broke into a nearby home, armed himself with two kitchen knives and cut off his ponytail with a pair of scissors. He held residents hostage until police took him into custody.

The Helzers and Godman were raised as Mormons, and Glenn and Justin had served their two-year missions. Glenn later married and has two daughters. The brothers, along with their mother, were excommunicated from the church in 1998.

Helzers' grandfather, Helmuth Helzer, told The San Francisco Chronicle the two brothers apparently got involved with drugs and that Glenn lost his broker job at Dean Witter and abandoned his family.

Bishop reportedly met Glenn Helzer at a ``rave'' concert. Local newspapers reported that she, the Helzers and Godman were active in the ``goth'' movement, dressing in dark colors and spending time in bars frequented by followers of occult activities.

Elvin Bishop, best known for his 1976 pop hit ``Fooled Around and Fell in Love,'' has not commented on the case, according to Mike Grill, who works for Alligator Records in Chicago.