KATY, Texas (CBSDFW.COM/AP) — Two drug store robbery suspects have been killed and two others arrested after investigators say officers returned fire during a surveillance operation in the Houston area.

Officials say the serial robbers were always after cash — not drugs.

READ MORE: Lewisville Police Search Called Off After Missing 10-Year-Old Simon Lian Found Safe

Harris County Sheriff Ed Gonzalez says the four men are believed responsible for at least a dozen robberies in the past two weeks. Members of a Joint Gang Task Force with the Texas Department of Public Safety (DPS) watched three men enter a Walgreens drug store Tuesday night and allegedly steal cash.

The trio and a driver sped off, stopped and then the suspects shot at pursuing officers — who returned fire.

READ MORE: Supreme Court To Hear Senator Ted Cruz's Campaign Finance Challenge

One suspect died at the scene. Another was pronounced dead at a hospital. Details weren’t immediately released on the two other suspects facing charges.

One DPS trooper suffered minor injuries from flying glass.

MORE NEWS: FC Dallas Welcomes Jesús, David Ferreira As 1st Father-Son Designated Players In MLS

(© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)