Lieutenant Craig Miller says they have several leads and have several persons of interest. Officers are trying to determine if it was only one shooter or multiple suspects.
Miller says they have potential video of the first shooting that killed a man in the city of Garland. The second shooting nearby damaged the cab of an 18-wheeler in Dallas, but the driver was not injured.
A third shooting killed 18-wheeler driver 42-year-old William Miller. The lieutenant called Miller's actions heroic because even though he was fatally wounded, he was able to control his big rig and not cause additional accidents.
Police say another 18-wheeler driver was injured when he was hit by flying glass as the bullet shot through the window.
Miller is asking anyone who may have witnessed the shootings in Dallas to come forward with information.
The suspect in the Garland shooting is described as a balding white man in his 40s, driving a tan F-150 with loud mufflers.
Schepps Dairy is offering a $10 thousand reward for information in the case.