Prosecutors say at least four Chicago boys who streamed the sexual assault of a 15-year-old girl live on Facebook threatened the victim with a dog if she tried to flee.

During a hearing Tuesday, Assistant State's Attorney Maha Gardner said a 14-year-old boy charged in the case told the victim she could "have sex the easy way or the hard way."

Also Tuesday, Judge Patricia Mendoza ordered a 15-year-old boy held in the Juvenile Temporary Detention Center while awaiting trial.

Both boys are charged with aggravated sexual assault and manufacturing and dissemination of child pornography.

Police say they expect other juveniles and an adult to be charged.

Police have said the assault was watched live by about 40 viewers, none of whom called authorities to report the attack.