CHICAGO (CBS) — Chicago police said Facebook needs to do more to prevent people from using the site to sell illegal guns and drugs, after a 10-month undercover operation resulted in 50 arrests and the seizure of at least 18 firearms and more than $46,000 dollars of drugs.

Police said, in February, a confidential informant contacted officers about illegal gun and drug sales being carried out on Facebook. The department’s narcotics unit launched a covert operation to infiltrate several secret Facebook groups that operated as virtual black markets.

“We didn’t know that these secret groups existed on Facebook,” Chicago Police Department Organized Crime Bureau Chief Anthony Riccio said. “The size of the marketplace is considerable. There’s dozens and dozens of these secret groups; a lot of them being used for illegal things, including the trafficking of the guns and the firearms, but there’s dozens of them out there.”

Since February, police have arrested 50 people who were selling guns or drugs through the secret Facebook groups, and have issued arrest warrants for 18 more. While the vast majority have previous criminal records, at least six did not, including a Chicago Public Schools teacher who was selling drugs on Facebook.

Riccio said the teacher was in possession of paraphernalia used to measure and distribute drugs when he was arrested at Leland Elementary School.

That CPS employee has been identified as physical education teacher Daniel Caponigri, 38, who has been on the job three months.

dan Cops Seize Guns, Drugs Sold Through Secret Facebook Groups

Daniel Caponigri (Chicago Police Department)

Police said, although officers contacted Facebook about their operation, the company did not help with the investigation.

Supt. Eddie Johnson said Facebook has a responsibility to make sure users can’t set up illegal black markets on their site.

“That’s a billion-dollar industry. Certainly they can spend a little money to ensure that these types of things don’t happen,” Johnson said. “The job of the criminal is to ply their trade and not get caught, right? They’re going to use any vehicle they can to do that. Our job is to catch them. Facebook has a responsibility to the people that they serve to ensure that these types of things don’t go on, and quite frankly they haven’t been very friendly to law enforcement to prevent these things.”

Facebook says it does not sanction illegal activities on its platform and has guidelines for law enforcement agencies that are conducting investigations.

Police said the gun and drug dealers who set up the secret Facebook groups are very protective about who is allowed to join.

“It’s not visible on someone’s Facebook page. You have to be invited into it, and the groups are so tight that they actually require people to vouch for you. So when you were introduced to the group, they’d say ‘Yeah, I know this guy. He’s not the police,’ or ‘I know this guy, he’s okay. So they’re very tight to protect the industry,” Riccio said.

Undercover officers were able to infiltrate the groups to set up the purchases of guns and drugs, and then carried out raids.

Riccio said the criminals who used Facebook to ply their trade felt a sense of security by setting up invitation-only groups to advertise the guns and drugs they were selling.

“It’s discreet. They’re able to hide their activities. They feel pretty confident that it’s a secret group, and the police aren’t going to be able to infiltrate it to find out what’s going on. So they feel that they can kind of be under the radar,” Riccio said.

Police seized at least 18 guns through a series of raids, most recently Wednesday night. Many of the guns had their serial numbers removed, and some had extended clips. Riccio said most were fully loaded and ready to use.

“There’s a lot of it out there. I’m happy we were able to get these. These are guns that are winding up on the South Side, the West Side of the city; and being used in these gang shootings,” Riccio said.

Riccio said the gun and drug raids are just the first phase in an expanding investigation into the use of secret Facebook groups to hide criminal activity.

“There’s other illegal activities that are going on Facebook. We’re looking at potentially human trafficking, things of that nature as well,” he said. “There’s a lot of tentacles that are going out for this.”

The operation also led to the seizure of more than 17 types of drugs, with a total street value of more than $46,000, according to Riccio.