(NewsNation) — Authorities have arrested a total of 28 people in connection to the “cartel-style” massacre last month in Central California, as part of “Operation Nightmare.”

The operation has also seized illegal guns and drugs and is expected to make additional arrests, according to Tulare County Sheriff Mike Boudreaux.

The killings took place Jan. 16 in Goshen, California, about 170 miles north of Los Angeles. Six victims including a teen mother and her 10-month-old child were gunned down. Security cameras captured footage of the gunmen and some victims, showing the young mother making it over the fence before being executed in the street.

The victims were: Rosa Parraz, 72; Eladio Parraz, Jr., 52; Jennifer Analla, 49; Marcos Parraz, 19; Alissa Parraz, 16; and Nycholas Parraz, 10 months.

Authorities said they suspected the killings had gang and cartel involvement as two of the victims were identified as Sureño gang members. Two of the suspects initially arrested are members of rival Norteño gang.

The two suspected killers were arrested in early February, and since then, 26 additional arrests have been made by multiple agencies in a four-day sweep.

The two people first arrested for the killings, Angel Uriarte, 35, and Noah David Beard, 25, have pleaded not guilty to charges including six counts of murder. Detectives believe Uriarte has ties to a California prison gang.

Boudreaux says “Operation Nightmare” is continuing to crack down on gang and cartel activity, but that the problem goes deeper.

“This goes into our prison system, this goes into different levels of drug trafficking organizations up and down the Central Valley of California,” Boudreaux said.

Boudreaux said he believes the gangs are fueled by the Mexican cartels.

“There is absolutely some connection between the upper echelons of these California street and prison gangs and the Mexican cartels,” Boudreaux said. “Most street gangs, their revenue comes from selling illegal drugs, right? … They’re getting a lot of that product from Mexico.”

Boudreaux identified the Sinaloa and Jalisco New Generation cartels as being “heavily involved” in California, saying they take advantage of the highways and airports to work closely with the street and prison gangs.