A Harford County Sheriff official called it a "targeted" attack and said they were looking for a suspect who was driving a black 2000 Chevy Acadia with Delaware tags.
All five of those who were shot are employees of the Advanced Granite Solutions where the shooting occurred, officials said. They said the suspect is "associated" with the business, sheriff's officials said.
Those who were injured were in critical condition at the shock trauma center in Baltimore.
The suspect's name is Radee Labeeb Prince and he is 37 years old, sheriff's officials said. Authorities said they believe he is the only suspect and others are not involved.
Prince is considered to be armed and dangerous, officials said, and he has a criminal history although officials did not elaborate.
Sheriff Jeffrey Gahler called the shooting "one of the most heinous acts we've ever seen in our county."
The business park where the shooting happened is located in Edgewood, about 20 miles northeast of Baltimore, with auto body shops, part supply stores, hotels and storage units in the area.
Just before 10 a.m., a woman frantically answered the phone at a marble and tile supply store and said she was hiding under a desk. She said her boss was outside the store and couldn't get in because of the police activity.
"I'm not sure what's going on," she said before hanging up to take another call.
Larry Hunt, the manager of RE Michel Company, a heating and air conditioning parts business in the business park, said he and other employees were outside talking to a customer about 9 a.m. when they heard loud arguing.
He said it sounded like it was coming from a business about a half-block away. He didn't hear sounds of gunshots, he said.
Hunt said emergency vehicles came toward them with sirens on and employees were ordered inside and to stay on a lockdown.
By 10:15 a.m., he said, he and six other customers and employees were locked inside the store and could see emergency personnel outside. Some traffic appeared to be moving in the business park, which has only one entrance in and out.
"We were very nervous," Hunt said.
Several schools in the area were on a "modified lockdown" and said it was being done "out of an abundance of caution," according to Harford County Public Schools.
The Harford County Sheriff's Office contacted at least one neighboring jurisdiction this morning to help in searching for a suspect. Michael Holmes, a lieutenant for the nearby Cecil County Sheriff's Office, said his agency received a description of a suspect and deployed several officers to aid in the search. He said it is Harford County's investigation and he could not release any additional information.
"We've been contacted by Harford County in reference to looking for the suspect," Holmes said.
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