A gunman stormed a suburban Maryland business park Wednesday and shot five people, three of them fatally, before escaping, police officers said.
A manhunt was underway for 37-year-old Radee Labeeb Prince, who was associated with the granite business where the shootings took place, said Harford County Sheriff Jeffrey Gahler.
"This does appear to be a targeted attack, limited to that business," Gahler said as he confirmed there were three dead and two other victims who were transported to trauma centres in serious condition.
He did not explain Prince's exact association with the business.
While the sheriff told reporters that investigators do not believe anyone else was involved, "there's an individual out there on the loose who committed one of the most heinous acts we've ever seen in our county."
All five victims were shot with a handgun and were employees of the business, Gahler said.
The deadly attack in the town of Edgewood, about 23 miles (37 kilometres) northeast of Baltimore, is the latest mass shooting in a country where such killings have become commonplace.
On October 1, a gunman in an upper-floor casino hotel room opened fire on thousands of people gathered at an outdoor country music concert in Las Vegas, killing 58 and wounding more than 500 in the deadliest shooting in recent US history.
To date in 2017, there have been 285 mass shootings — defined as four or more people shot or killed, not including the shooter — in the United States or nearly one per day