[Former Proud Canadian]

Hammer, how do two drug gangs have a 15 minute gun battle in an American city and the cops don’t get involved?

[STD]

The shootout reportedly lasted 15 minutes with no casualties.

Better yet, how do they have a 15 minute shoot out without anyone getting hit?

[Bibman]

Cmon down with the rest of the snowbirds, and I will show you.
77 is full of Rv’s and three car tows going south. I am not a snowbird. I am from the the LRGV.
The cartels and Zetas go north and the snowbirds come south. They meet in the valley. Two weeks ago the Border Patrol
( La Migra) pulled two wets out from under my girlfriends house. The head roll across the dance floors and PERRY does NOTHING!

[Charles Martel]

...how do two drug gangs have a 15 minute gun battle in an American city and the cops don’t get involved?

Damn good question - and one that several Brownsville-area bloggers have asked in connection with this article. Here's the closest thing I could find (about halfway through the linked story):

Brownsville Herald, July 14th.