Konkoly, Steven. Garrett Mann series

After FBI special agent Garrett Mann executes a deadly raid on an underground facility in New Mexico, the sole survivor's testimony reveals a greater threat to come. The covert lair was a training ground for hundreds of cartel sicarios, who have since disappeared into the US, their ultimate mission still unknown. When another FBI raid goes catastrophically wrong, Mann finds himself on the trail of the Bureau's original target -- a moonlighting serial killer who leads the agent into a nightmare that's darker and more extensive than Mann ever feared. As Mann and his team hunt their fugitive, they find he could have deep ties to powerful government officials. But even as the list of people Mann trusts grows smaller, he must find the killer and blow the heart of this conspiracy wide open before more lives are lost