A gunman has opened fire at a Maryland office park, killing three co-workers and wounding two others, authorities and the business owner said.
A manhunt is under way for 37-year-old Radee Labeeb Prince, who is considered armed and dangerous.
Harford County Sheriff Jeffrey Gahler said Prince shot his victims with a handgun and fled Emmorton Business Park in Edgewood, 25 miles north east of Baltimore.
Mr Gahler said officers were on the scene within four minutes of the report of a shooting, but he did not release a motive for the shooting.
The victims and the suspect worked for Advanced Granite Solutions, the owner of the home improvement company said. Prince had been an employee for four months, working as a machine operator, owner Barak Caba said.
The wounded are in critical condition, according to a spokeswoman for University of Maryland Medical Centre's R Adams Cowley Shock Trauma Centre in Baltimore.
Maryland governor Larry Hogan said the survivors had gunshot wounds to the head.
He said authorities had helicopters in the air and police on the ground looking for Prince, who may be driving a black 2008 GMC Acadia.
"The killer remains on the loose," Mr Hogan said.
The FBI is assisting local authorities. Investigators are treating the shooting as a case of workplace violence and did not see ties to terrorism, said Dave Fitz, a spokesman for the Baltimore FBI field office.
Nearby schools and businesses were locked down as a precaution.
The business park is just south of the Interstate 95 interchange with Maryland 24.
Yellow crime scene tape cordoned off Advanced Granite Solutions on Wednesday afternoon. Investigators, officers and federal agents fanned out across the business park to investigate.
Across the road, several employees, some wearing lime green T-shirts with the Advanced Granite Solutions logo, embraced each other as they waited for news of their colleagues.
The sheriff said the department had set up a receiving area for family members in a nearby hotel ballroom.
He said Prince had a criminal record, but he did not know the extent of it. According to online court records, Prince lived in Elkton - about 35 miles from the shooting scene - as recently as last month.
The sheriff said authorities checked an Elkton home after the shooting, but Prince was not there.