Allen, a 15 year veteran of the department, leaves behind a wife and three children.
A Texas state trooper has been shot and killed in Freestone County, the Navarro County Office of Emergency Management confirmed in a tweet Thursday afternoon.
Authorities say the gunman is Darbrett Black.
Allen, 41, was making a routine traffic stop on Interstate 45, just south of Fairfield, Thursday, when Black allegedly shot him with a rifle and sped away.
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The Texas Department of Public Safety and other law enforcement agencies identified the suspect as 32-year-old Dabrett Black.
Black has been charged with capital murder of a police officer, and is being held at the Brazos County Jail. He faced charges of first-degree felony, aggravated assault against a public servant and evading arrest, a third-degree felony.
Following news of the trooper's death, Waller County Sherrif's Office said on Facebook that they were saddened by the death of a "brother". The trooper died at the scene.
"Trooper Allen's dedication to duty, and his bravery and selfless sacrifice on this Thanksgiving Day, will never be forgotten". After the trooper returned to his patrol unit, DPS officials believe the suspect fired multiple shots at the trooper.
"This morning and the days to follow please continue to keep Trooper Allen's family, friends and coworkers in your thoughts and prayers". Freestone County is about 90 minutes southeast of Dallas.