Harford County Sheriff Jeffrey Gahler identified the shooter as 37-year-old Radee Labeeb Prince. He said Prince opened fire with a handgun and then fled the Emmorton Business Park in Edgewood.
Police were looking for him, and he was considered armed and dangerous. The sheriff did not release a motive for the shooting.
The owner of a home improvement company in the office park said the victims and the suspect all worked for him at Advanced Granite Solutions.
Barak Caba told The Associated Press in a brief telephone interview that the suspect has been an employee for four months. He said the man was a machine operator.
Caba was shaken and would not provide additional details.
The wounded were in critical condition, according to a spokeswoman for the University of Maryland Medical Center's R Adams Cowley Shock Trauma Center in Baltimore.
The FBI is assisting local authorities to find Prince. Investigators are currently treating the shooting as a case of workplace violence and don't see ties to terrorism, said Dave Fitz, a spokesman for the Baltimore FBI field office.
Nearby schools have been locked down as a precaution.
The business park is just south of the Interstate 95 interchange with Route 24.