Granat's parents, Maria and John Granat, were found bludgeoned and stabbed to death last month in their home in unincorporated Palos Township, Ill.
The Cook County Sheriff's Department said Christopher Wyma, 17, of Bridgeview, Ill., Mohammad Salahat, 17, of Chicago Ridge, Ill., and Ehab Qasem, 19, of Hickory Hills, Ill., have allegedly admitted their roles in the killings.
The three teens allegedly confessed Sunday to carrying out a pre-arranged plan to kill Granat's parents and steal thousands of dollars from the couple, the sheriff's department said Tuesday in a release.
Wyma and Salahat are seniors at Amos Alonzo Stagg High School, where 17-year-old John Granat was also a senior. Granat was charged last month with two counts of first-degree murder for his role in the deaths of his parents. Qasem is a 2011 graduate of Stagg High.
Salahat, Wyma and Qasem allegedly told investigators they, along with Granat, went upstairs around 2 a.m. on Sept. 10 and found Granat's parents asleep in bed. Salahat, Wyma and Qasem then allegedly began beating the victims with baseball bats, while John Granat allegedly stabbed his mother to death.
Granat then allegedly gave the other three some of the thousands of dollars in cash that was in his family home.
The Cook County Sheriff's Department said Salahat, Wyma and Qasem provided detailed, videotaped confessions and provided investigators with directions to where the alleged murder weapons could be found.
Granat is being held without bond in the psychiatric wing of the Cook County Jail.