Four banks robbed in four hours in fourth largest US city

Houston, whose skyline is pictured here, is America's fourth-largest city.</p>

Houston, whose skyline is pictured here, is America's fourth-largest city.

Today was a busy day for bank robbers.

Four banks were robbed in four hours in Houston, America's fourth largest city.

The timing was just a coincidence, and federal investigators don't believe the crimes are linked, Houston's ABC affiliate said

The first robbery happened around 10:30 am local time at a Wells Fargo branch. The second happened less than an hour later at another Wells Fargo location. The third robbery was just before noon at a BBVA Compass Bank about 50 yards from a Houston police station. 

One shot was fired into the air in that robbery, Houston's ABC station reported. 

The last bank robbery happened at a Chase Bank branch at around 2:30 pm. 

An investigation is ongoing, the Houston Chronicle said