But work continues to determine if any of about 100 other people named in the stream of tips may have been involved in the killings of 14-year-old Liberty German and 13-year-old Abigail Williams.
"These are people where information has come in to us saying, 'Hey I think that looks like this person,'" he said. "Those are people we're still following up on, trying to check out their stories."
The girls vanished Feb. 13 while hiking along a trail near Delphi, about 60 miles northwest of Indianapolis, on a day off school. Their bodies were found the next day in a rugged, wooded area near a stream east of the city of about 3,000 residents.
Investigators had received more than 13,000 tips by Monday, and about 2,200 of those still must be pursued to determine whether or not they are relevant to the case, Riley said.
Authorities saw a surge in tips after German's grandfather, Mike Patty, pleaded with the public last Thursday to provide information in the case. Riley said the number of new tips flowing in has since declined but still numbers more than 200 a day.
Patty urged the public during a news conference to study two grainy images of a man considered the main suspect in the killings and audio of a male saying "down the hill."
That evidence came from German's cellphone, and police have hailed her as a hero for recording potentially crucial evidence.
Police have been tight-lipped about details in the case, and have not disclosed how the girls were killed or whether investigators collected DNA from the crime scene.
Carroll County Prosecutor Rob Ives said about 70 subpoenas and three search warrants had been issued and served in connection with the case as of Tuesday.
While the month-old investigation has lost some officers to other cases, Riley said more than 40 officers, including FBI agents, are still working the Delphi killings every day.
Carroll County Sheriff Tobe Leazenby said investigators remain confident the murders will eventually be solved, but are still looking for the tip that will break the case.
"I'm operating from the standpoint where the next phone tip or email tip is the one we've been searching for. That's what we operate on, day in and day out," he said.