There are 11 identified gangs in Harlingen, some of which police describe as extremely dangerous.
Sgt. Stephen Mayer heads the Harlingen Police Department TMs Gang Eradication Unit.
He remembers how gangs terrorized parts of the city just two years ago.
"This all came to a head with the shooting of Officer Diaz, said Mayer.
Sgt. Mayer said gang violence in the city has fallen 79 percent in the past two years, partly at a cost to other Rio Grande Valley cities.
"What I think our biggest contributor to the reduction in gang violence is the fact that a lot of our gang members have moved out of Harlingen and into other communities in the Rio Grande, said Mayer.
Mayer said the work of his team is responsible for the decrease.
Working at different days and hours every week, the Harlingen Gang Eradication Unit will patrol city streets, scrutinizing known gang members for breaking any law, no matter how minor.
"Even for jaywalking, said Mayer. "You bet there are quite a few gang members who have gone to jail for walking in the street when there was a sidewalk provided, which is against the law."
But it TMs this level of scrutiny that Mayer said has parents upset, asking why police are picking on their children.
"A lot of the times | some parents may not understand the consequences of gang involvement, Mayer said. They may not realize how dangerous of a lifestyle this is."
Action 4 News accompanied the Harlingen Gang Eradication Unit on a recent Friday night.
At one point, two teens were stopped, walking down a street where a car alarm went off.
The teens said police are always badgering them.
Nonetheless, one boy was found violating his probation, while the other was found with a knife.
That night, Harlingen police made five arrests; two of them were gang-related.
A known Westside gang member, 17-year-old Hector Aparicio, was arrested after a fight with a girlfriend apparently prompted him to break a window, leaving blood and shattered glass on the sidewalk.
Police officers allegedly found marijuana in his apartment.
Mayer said arrests like this are what encourage gang members to get out of their gang or get out of town.
But there is help for those hoping to get out.
Mayer said the police department can arrange job placement and even counseling.