Federal investigators are trying to break Houston's reign as the nation's leader in armored car robberies and bank holdups.

Statistics show that 11 armored trucks were robbed in Houston in 2013 and another eight last year. Early this year, a Brinks employee was fatally shot in a daylight robbery in one of the city's busiest areas. That case remains unsolved despite offers of $100,000 rewards.

Last year, 100 banks were robbed in the Houston area, comparable to other big cities. But 40 percent of them were takeover holdups, in which the robbers hold staff and customers are gunpoint.

Law enforcement has had some success in catching up with the criminals but has not been able to determine why Houston has become a hub for these types of crimes.