UPDATED 10/11/11 10:05 p.m.

PALOS TOWNSHIP, Ill. (CBS) — Three suburban teenagers have been charged with helping a high school classmate kill his own parents in unincorporated Palos Township last month.

Christopher Wyma, 17, of Bridgeview; Mohammad Salahat, 17, of Chicago Heights; and Ehab Qasem, 19, of Hickory Hills, are each charged with first-degree murder in the slayings of John Granat, 44, and his wife, Maria Granat, 42.

Bond for all three new defendants was denied Tuesday morning by Judge Peter Felice Bridgeview Courthouse.

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John and Maria Granat were found beaten and stabbed to death Sept. 10 in their home in the 12700 block of 81st Court in unincorporated Palos Township. Their son, also named John Granat, 17, initially called police to report that his parents had been murdered, but he was charged with the murders shortly afterward.

Wyma and Salahat are both seniors at Amos Alonzo Stagg High School in Palos Hills, where the younger Granat also attended. Qasem is a 2011 graduate of Stagg and a friend of the defendants, according to the Cook County Sheriff’s office.

As CBS 2’s Mike Puccinelli reports, the defendants are charged with carrying out a premeditated plan to rob the Granats of thousands of dollars in cash.

“They went up to the bedroom where John and Maria Granat were sleeping and there they viciously murdered them,” Cook County Sheriff Tom Dart said. “They beat them with bats, stabbed them with knives.”

Authorities also said that, hours before the murders, the teens had met to plan out their scheme and came up with a code word to use to set their plan in motion: concert.

Granat allegedly gave the signal in a conversation with his friends on the night of the murders, prompting them to come to the Granat house to carry out their plan.

Police said John Granat Jr.’s hatred of his parents was one motive behind the plot the killers carried out last month.

Prosecutors said $35,000 in cash stored in the home was the other motive. It’s money that Granat Jr. went to retrieve, shortly after the initial attack, when his accomplices came downstairs from the bedroom with some disturbing news.

“They said one of the victims, the mother, was still making noises – at which time, John told them to go upstairs and finish them off,” Dart said.

A fourth defendant, Mohammed Salahat, was also accused of murder. Investigators said he drove the getaway car.

His attorney said his client was just 16 at the time of the crime.

“I don’t think his statement that he made would be reliable, given the fact that he was only a child of 16 and interrogated several times by big policemen with guns,” attorney Joel Brodsky said.

Wyma’s attorney said his client’s parents are stunned by the allegations.

“They’re absolutely shocked about the allegations,” attorney John Russell said.

Granat Jr. originally told police that he had fallen asleep in the basement of the home around 12:30 a.m. Sunday, and was home the entire night. He claimed he woke up to find the house ransacked, and when he went to wake up his parents for church, they were dead.

Maria Granat was stabbed repeatedly while in bed, while John Granat Sr. was beaten to death and was found lying on the floor at the side of the bed, according to the sheriff’s office.

But police say the younger Granat’s initial story was proven to be untrue. It turned out that he had been pulled over by Palos Heights police for a minor traffic offense at 122nd Street and Harlem Avenue at 5:17 a.m. that morning, sheriff’s police said.

Sheriff’s police said several conflicting stories came out of Granat Jr.’s mouth, until finally, he told investigators that he had needed money, and let a friend come into the house while he was out. Granat Jr. said he fell asleep in his own car and didn’t come in until 7 a.m., when he found his parents dead, according to sheriff’s police.

But sheriff’s police concluded that Granat Jr. himself was the killer, and found out from several friends that he had threatened to kill his parents several times before.

Granat Jr. later said he had been with Wyma, Salahat and Qasem, but they denied his claims when first questioned. But investigators pursued leads even after Granat Jr. had been charged, according to the sheriff’s office.

On Sunday, sheriff’s investigators began questioning the new defendants and they finally admitted to the crime.

Salahat told detectives he drove Wyma and Qasem to the Granat home and Granat Jr. let them in around 2 a.m. The three told investigators they went upstairs with Granat Jr. and found his parents asleep in bed.

At the bond hearing Tuesday, Cook County Assistant State’s Attorney Peter Troy said Granat Sr. awoke and tried to defend himself. Meanwhile, prosecutors said, Qasem stabbed Maria Granat with a knife that had been in the house and then Granat Jr. continued to stab his mother, the Sun-Times Media Wire reported. They also beat both victims with baseball bats, authorities said.

After the victims were killed, Granat provided the other three with some of the thousands of dollars in cash his parents had kept in the home, according to the sheriff’s office.

Investigators believe the teens split $35,000 they found in the home, of which about $21,000 has been recovered, the Sun-Times Media Wire reported.

After the attack, the group went to Wyma’s home to clean the weapons and burn the gloves they wore, the wire reported. They discarded the weapons and their clothes in forest preserves and other locations, according to the sheriff’s office.

A knife, baseball bats, clothing and cash were later recovered.

All four defendants were being held without bond in the psychiatric wing of Cermak Hospital at Cook County Jail. Cook County Sheriff’s office spokesman Steve Patterson said all four have requested protective custody, meaning they will be housed alone.

They will remain at the jail’s hospital until hospital staff determines they can be housed in the general population. When that happens, they will be housed in a maximum security area of the jail, in protective custody.