A Jewish supermarket in New Jersey was the target of a gun attack which left six people dead including two suspected assailants, say officials.
No motive has been confirmed, but the mayor of Jersey City tweeted that "hate and anti-Semitism" had no place in the city.
The suspects are believed to have killed a detective across town, then driven a rental van to the store.
Security video shows them firing on the market before going inside.
Investigators believe that the three people found dead inside the kosher market were killed by the attackers, who were also found dead inside the building following a four-hour standoff with police on Tuesday.
An additional victim was injured, but managed to escape, authorities said on Wednesday.
The mayor of Jersey City, Steven Fulop, told reporters that street cameras showed two people "slowly" drive towards the market, then "calmly open the door with two long rifles and begin firing from the street" into the shop.
Public safety director James Shea said video showed they parked their van "and immediately began firing on the location". Asked how police were certain that the shop was targeted, he said the men had "bypassed" many other people walking on the street to attack the store.
The attackers have been identified as David Anderson, 47, and Francine Graham, 50.
Sources tell NBC that Anderson was a follower of the Black Hebrew Israelite movement, whose believers say they are the true descendents of ancient Israelites.
A neighbour told NBC that Graham was a former home carer in Manhattan and had met Anderson after she got hurt at work.
The New York Times and New York Post reported on Wednesday that one of the suspects had made anti-Semitic and anti-police social media posts online before the attack.
How did the attack unfold?
The violence began at a cemetery about one mile (1.6km) away from the grocery store.
The suspects killed Detective Joseph Seals, 39, who approached them for questioning about the murder of an Uber driver over the weekend, New Jersey Attorney-General Gurbir Grewal said.
The pair fled the scene in the van and drove to the kosher supermarket at 12:20 local time (17:20 GMT) where they held off armed police and federal officials for four hours, shooting off hundreds of rounds of ammunition.
The attackers had opened fire on the shop before entering, alerting two officers on foot patrol who began firing at the suspects until they were injured by the attackers' gunfire.
On Wednesday, the Jersey City Mayor Fulop said "had they not been there and not responded, more people would have died".
Mr Grewal said officials were "not in the position at this time to say definitively why the suspects decided to stop in front of the supermarket and begin firing immediately".
"This is one of the biggest gunfights I've seen in a while," Willy McDonald, 67, told the New York Times. "And I've been in Vietnam."
An active pipe bomb was found in the suspects' vehicle, police say. Reports indicate that a rambling note was also left inside for police to find.
The incident ended just before 16:00 when officials used an armoured vehicle to ram through the front entrance of the shop and found the bodies of the attackers.
The attack put approximately 30,000 students on lockdown, unable to leave their classrooms for hours after the school day had ended. Class start times were delayed on Wednesday.
Who are the victims?
The three victims inside the shop were killed soon after the gunfire broke out, but one managed to escape after being injured.
They have been identified by New Jersey officials as Mindy Ferencz, 32; Miguel Douglas, 49 and Moshe Deutch, 24.
"Mindel Ferencz, may she rest in peace, was a pioneer," said Rabbi David Niederman, who first confirmed the death of the mother of five.
"She was a lady full of love for others," he added. "Unfortunately, her life was cut so short."
Ferencz's mother told the New York Times that her husband, who owned the supermarket, had taken a break from work to go to a nearby synagogue minutes before shots rang out.
Deutsch's death was also confirmed by Rabbi Niederman, who hailed him as a student who worked to organise a food drive that provided help to 2,000 families each year.
What has been the response?
New York City Mayor Bill de Blasio called the attack a "hate crime" and an "act of terror" and ordered police on high alert, especially in Jewish communities. Jersey City is part of the New York metropolitan area.
"This confirms a sad truth. There is a crisis of anti-Semitism gripping this nation. There is a crisis of anti-Semitism in this city," he said in a Wednesday news conference.
He added: "History tells us to take these warning signs seriously."
New York Police Department commissioner Dermot Shea added that hate crimes in New York City were up 22% this year.
"You see a swastika being drawn, you see a brick being thrown through a window, you see a woman walking down the street with her kids and having her wig ripped off," he said.