(AP) — Authorities in Omaha have arrested four men on suspicion of gang-related activity that includes gun and drug trafficking.

Local and federal authorities made the arrests Thursday as part of a nine-month investigation called Operation Purple Haze. It included undercover officers buying drugs, as well as tips from the public.

Authorities are now trying to find several other men wanted on drug charges.

Omaha Police Chief Todd Schmaderer says all the men are considered leaders in two of the city’s most notorious crime rings. He called the arrests “a major bust.”

Police have identified more than 70 gangs in Omaha.