Details of the arrests were announced at a Saturday evening news conference outside police headquarters. Police Director Irving Bradley said detectives had been working around the clock since the crime was reported March 28.
Those arrested included , 20, in custody since last week, when he was charged with having sex with the 15-year-old. The other four are Timear Lewis, 19, and boys ages 13, 14 and 17. Each was charged with aggravated sexual assault and child endangerment.
Prosecutors likely would seek to try all of them as adults, Mercer County prosecutor Joseph Bocchini said.
The case shocked residents of the gritty Rowan Towers apartment building, where three of those arrested live, police Capt. Joseph Juniak said.
Building management has stepped up its security presence there and promised additional safety measures. Residents have expressed skepticism that the apartments would become safer.
Police say the 15-year-old girl went to a party with some men at Rowan Towers on March 28 and the younger girl tagged along because she was worried about her stepsister's safety. They say the 15-year-old sold sex to men and boys there, then took money to let them touch the younger girl. They say the touching turned to forcible sex as at least seven men raped the 7-year-old.
Additional arrests are expected, police said.
Before Saturday's arrest announcement, the 15-year-old had been charged with promoting prostitution, aggravated sexual assault and other crimes. Police have not released her name, and she remained in juvenile detention Saturday night.
MORE ON CRIMESIDER