A trooper and the suspect were wounded and hospitalized, according to Lt. Col. Bill Dofflemyer of the Maryland State Police.
Investigators have not yet established a motive for the workplace shooting, which occurred at about 2:30 p.m. ET, Washington County Sheriff Douglas W. Mullendore told reporters at a briefing.
The Washington County State’s Attorney’s Office is working to determine charges for the suspect, who is not being named at this time, according to a news release from MSP.
The wounded state trooper, who is a 25-year veteran of the agency, was treated for his injuries and released, according to an update from MSP. The suspect was also wounded after at least one of the troopers who responded to the scene returned fire and struck him. He was still being treated Thursday evening, police said.
Police from the nearby town of Smithsburg were first to arrive at the plant and discovered one victim in a field near the business, Mullendore said. A news release from the sheriff’s office said there were four victims total at the plant, three of whom were dead.
State police received a description of the suspect and his vehicle, and three troopers found him driving about 5 miles from the shooting scene.
“When troopers went to stop the vehicle, the suspect immediately started firing multiple (bullets) at the troopers,” Dofflemyer said. A pistol was recovered at the second shooting scene, authorities said.
The sheriff identified the victims who were killed as Mark Alan Frey, 50; Charles Edward Minnick Jr., 31; and Joshua Robert Wallace, 30. The other victim was Brandon Chase Michael, 42; police earlier said he was critically injured.
Smithsburg is about 75 miles west of Baltimore. It is about 100 miles from the border with West Virginia, where the suspect lives, according to the sheriff.
The Washington County Sheriff’s Office is leading the homicide investigation with help from the FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives office in Baltimore, according to MSP.
Any troopers involved with the shooting “will be placed on administrative duty” until the investigation is complete, per agency protocol, MSP said.
CNN’s Mike Valerio, Michelle Watson and Joe Sutton contributed to this report.