The Instagram account called "rats215" has since been removed from the photo-sharing site but by whom is unclear.
"In my mind it's criminal. It's the same as witness intimidation," said Commissioner Charles Ramsey.
Many of the documents and names revealed on the popular site are not public record.
Investigators want to know the source of the information.
"Most are pretty old cases, some are not. Some had information that had been redacted, some did not have redactions. We are in the middle of the investigation," said Commissioner Ramsey.
A law enforcement source says a 17-year-old has been identified as a suspect.
He's expected to be arrested for witness intimidation related to a grand jury investigation. His name has not been released.
Investigators say building a broader case can be tough due to free speech rights and the difficulty proving who actually downloaded the material.
Commissioner Ramsey has seen sights like this in other cities and he says it needs to stop.
"It's just a terrible thing for someone to do to potentially put someone else in jeopardy. I think this goes way too far and if there's legal action that can be taken, we will pursue it," he said.
Commissioner Ramsey says no witnesses have been directly threatened as a result of the web page.