Police arrested a man suspected of killing three people and wounding two on Wednesday at a Maryland business park before shooting another person in neighboring Delaware.
Radee Prince, 37, was caught as he fled on foot in Delaware after a manhunt that saw local Maryland schools in lockdown and the nearby set of Netflix drama House of Cards reportedly sealed off.
Police said the latest mass shooting to hit the United States was a "targeted attack".
"At 7:05 pm (2305 GMT), a suspect was taken into police custody after a brief foot chase," Wilmington, Delaware Police Chief Robert Tracy told a televised news conference.
Prince discarded a .380 caliber firearm during the chase -- the same caliber used in the shootings, though ballistics testing still needs to be done to conclusively determine if it is the same weapon, Tracy said.
The police chief had earlier told reporters that Prince was "a dangerous individual. This person shot six people in one day," in attacks that were not random.
Prince was sought "in connection with both a multiple shooting incident early this morning in Edgewood, Maryland and another shooting incident at mid-morning today" in Wilmington, a statement from police said.
Harford County Sheriff Jeffrey Gahler said three people died in the first incident at a granite business just before 9:00 am (1300 GMT).
He confirmed a handgun was used and two other victims were transported to trauma centers in serious condition.
Gahler said Prince was associated with the company, Advanced Granite Solutions, where the first shooting occurred, near Baltimore.
"This does appear to be a targeted attack, limited to that business," he said.
Police were investigating Prince's connection with the firm, where all five victims of the first shooting were employed, Gahler said.
He said other people besides the five victims were on the premises when the shooting took place.
Tracy said the victim in the second shooting identified the gunman.
"They're known to each other and they've had some past history," he told a news conference.
The suspect fled the first attack in a car registered in Delaware, Gahler said.
Variety magazine reported that the set of "House of Cards," which is partly filmed in Maryland, was placed on lockdown while police searched for the shooter.
The executive producer of the series, Dana Brunetti, said on Facebook: "Shooting near House of Cards set."
Several schools in Maryland were also placed on lockdown while the shooter was still at large, officials said.
The incident was the latest mass shooting in a country where such killings have become tragically commonplace.
On October 1, a gunman in a 32nd-floor casino hotel room rained fire down on concert-goers in Las Vegas, killing 58 and wounding more than 500.
It was the deadliest shooting in recent US history.
The Las Vegas shooting sparked efforts to ban "bump stocks," a device that allowed the firing of a semi-automatic rifle close to the rate of a fully automatic weapon.
But broader gun control measures remain staunchly opposed by Republicans, with the backing of the powerful National Rifle Association lobby.