NEW YORK (NYTIMES) - Police officers shot and killed a black man who was known to be mentally ill on a Brooklyn street corner on Wednesday (April 4) after he pointed what the officers believed was a gun at them, the authorities said. The object turned out to be a metal pipe with a knob on it.

The shooting drew a charged crowd of dozens to the streets of the Crown Heights neighbourhood. The city Police Department had encountered the man before and classified him as emotionally disturbed, and the shooting raised questions about what the officers on the scene knew about him.

Five officers - three of them in street clothes, and two in uniforms - were responding to three 911 calls about a man threatening people with a silver gun, Terence Monahan, the chief of department, said at a news conference. A law enforcement official who listened to one of the calls said a woman was frantically reporting that a man was pointing a gun at people.

The police found a man who matched the descriptions from the 911 callers, Monahan said.

"The suspect then took a two-handed shooting stance and pointed an object at the approaching officers," Monahan said.

Monahan said four of the officers - the three in street clothes and one uniformed officer - fired 10 bullets in all. The man was pronounced dead after being taken to Kings County Medical Center. His name was not immediately released but a law enforcement official and some local residents said he was Saheed Vassell, a man in his 30s described as a familiar figure on the corner and a caring father of a son.

In an interview with NY1, Eric Vassell, whom the station identified as the dead man's father, said that his son had bipolar disorder and did not cause any trouble.

Vassell, an immigrant from Jamaica, said he did not know how to explain the shooting to his granddaughter, the dead man's niece. "She just don't understand," Vassell said.

Area residents said Saheed Vassell begged for money in a nearby subway station and did odd jobs for shopkeepers. He loved to dance and was widely known to be mentally ill. People said he had a penchant for picking things up off the street - cigarette lighters, empty bottles and other debris - and playing with them like toys.

John Fuller, 59, said that he had known the man for years and that police officers had, too. He echoed a common refrain: The officers should have known him well enough to not simply shoot him to death. "Every cop in this neighbourhood knows him," he said.

The police said that he had been arrested before and that officers had classified him as an emotionally disturbed person in previous encounters.

The police released blurry still images from surveillance videos of a man with an outstretched arm. The police said they showed him pointing an object that appeared to be a gun at people on the street and then pointing it in the officers' direction after they arrived. They also released a picture of what the man turned out to have been holding: a slim, curved silver pipe with a cylindrical knob at the end of it.

Witnesses said the officers appeared to fire almost immediately after they got to the corner around 4:45 p.m. Some of the witnesses said they did not hear the officers say anything to the man before firing, while another witness said she heard the officers and the man exchange some words.

The police did not answer questions about whether the officers had said anything before firing.

Dozens were still gathered at the scene late on Wednesday. "Murder!" some bystanders shouted at dozens of police officers behind yellow tape. Other crowd members wept at how this had happened on the 50th anniversary of Martin Luther King Jr.'s assassination. Others spoke of wanting to riot. When darkness fell, a group of around 10 protesters arrived carrying Black Lives Matter signs.

Jaccpot Hinds, 40, said he was walking in the area when he saw an unmarked police car pass him and pull across two lanes of traffic near where a man was standing on a street corner. Hinds said a plainclothes officer got out of the passenger seat of the car and fired at the man numerous times. The officer appeared to shoot him in the neck, chest and right arm, Hinds said, and then walked over to the man and prodded his chest with the service weapon.

Hinds said that officer, joined by two other plainclothes officers who had been in the car with him, tried to resuscitate the man.

The police did not immediately release surveillance video from the scene, and Monahan said the officers who fired had not been wearing body cameras. Monahan said that the plainclothes officers were part of an anti-crime unit and that the uniformed officers belonged to the Strategic Response Group, which is assigned to major events and criminal hot spots. The names and races of the police officers were not released.