Authorities took one person into custody but were still searching for a man believed to be the shooter, Houston Police Executive Assistant Chief James Jones told reporters
The Harris County constable deputies were working at the 45 North Bar and Lounge when they responded to a disturbance outside the business around 2:15 a.m., Jones said.
They were trying to arrest someone when another person with a rifle ambushed them and opened fire on the deputies from behind, Jones said, according to preliminary information from the scene.
One deputy was shot in the back and another was shot in the foot, said Mark Herman, Harris County Constable Precinct 4. The third deputy was pronounced dead at the hospital.
It was unclear whether the deputies returned fire, Jones said. He said Houston police were still investigating, but authorities believe the disturbance may have been a robbery that the constables stopped.
A person of interest was taken into custody at the scene, but authorities were not certain whether the person was a suspect or a witness.
Constables are licensed peace officers who perform various law enforcement functions, according to the Texas Association of Counties.