The deaths included two police shootings, one of which was streamed live on Facebook, and an officer fatally striking a pregnant woman with his car.

The police in Indianapolis on Thursday faced mounting pressure to provide answers for a traumatic eight-hour stretch in the city in which police officers killed three people: a man shot by the police while he streamed the encounter live on Facebook; a pregnant woman who was fatally struck by an officer’s car; and a 19-year-old man who may have called 911 to lure the police to an apartment before firing at them.

Hundreds of protesters gathered downtown and at the scene of one of the shootings, a rare display of public grief and outrage in a state still largely shut down because of the coronavirus. Although the number of people killed by police officers in the city has dropped sharply in recent years, the string of deaths — and the harrowing circumstances of each — set off renewed scrutiny of the Indianapolis Metropolitan Police Department.

Much of the protesters’ anger was directed at the first of the three encounters, in which Dreasjon Reed, 21, was shot and killed while running from a police officer after a car chase on Wednesday evening. Mr. Reed, whom the police said they pursued after seeing him nearly hit several cars, was streaming live on Facebook during the chase, and thousands of people were tuned in when he was shot.

Randal Taylor, the police chief, said on Thursday that a gun was found near Mr. Reed and that it had been fired twice, but that it was not clear “which shots were fired when.” Activists remained skeptical of the police account, and despite Mr. Reed’s video, critical questions remained unanswered; much of the encounter took place off-camera and the police said no body or dash cameras had recorded the killing.

The video did capture a morbid joke from a detective, out of view of the camera, after Mr. Reed was shot. “Think it’s going to be a closed casket, homie,” the detective said, apparently referring to Mr. Reed’s funeral. Chief Taylor said disciplinary action would be taken against the detective and called the comments “unacceptable.”

At the protests on Thursday, some who considered the killing unjust called for charges against the officer and said it followed a pattern for the Police Department, despite recent progress. It also recalled the death of Philando Castile, whose girlfriend recorded him on Facebook Live as he was dying after being shot by a police officer in Minnesota.

Erica Bailey, whose father was killed by Indianapolis officers after a police chase in 2017, said watching the video of Mr. Reed’s death had left her devastated again.

“This broke my heart,” Ms. Bailey said of Wednesday’s shooting. Her advice to the demonstrators: “Don’t give up.”

“Don’t give up, y’all hear me? Because I know the pain.” – Erica Bailey, daughter of Aaron Bailey who was killed by police in 2017. pic.twitter.com/xDTlJZpg3x

— Justin L. Mack (@justinlmack) May 7, 2020

After the shooting of Ms. Bailey’s father, Aaron Bailey, who was unarmed, the police chief at the time called for the officers who shot him to be fired. They were cleared by a civilian review board in 2018, The Indianapolis Star reported.

On Thursday, protesters also gathered at the intersection in the northwest part of the city where Mr. Reed had parked his car before he was shot nearby. They blocked traffic, chanted and occasionally feuded with officers despite a plea from the local N.A.A.C.P. branch to avoid gathering in large groups because of the risk of falling ill with the coronavirus, though many wore masks.

Wednesday’s chase began when the department’s chief and deputy chief, who were each driving in an unmarked car, noticed Mr. Reed driving recklessly and sought to pull him over. Mr. Reed continued to drive and began recording himself on Facebook Live, saying he did not want to go to jail and pleading with someone to come get him. The car chase was called off because supervisors deemed it too dangerous, but as Mr. Reed left the car and fled on foot, another nearby officer ran after him, shooting and killing him.

Chief Taylor said at a news conference on Thursday that, in total, 15 shell casings had been recovered from the two guns, seemingly indicating that the officer had fired 13 shots. A series of loud bangs can be heard on the Facebook video around the time Mr. Reed falls to the ground, with most coming after he had fallen. The police said the officer had also tried to use his Taser.

The officer was uninjured and has not been identified, but the police said that he and Mr. Reed were both black men, and that they were the only people at the scene during the encounter.

Mr. Reed, who was sometimes known as Sean, had served with the Air Force for about nine months in 2017 and attained a rank of airman first class, a spokesman for the Air Force said. Family members told The Star that he was always smiling.

“To see your son get shot and killed on FACEBOOK Live is a different kind of hurt,” his mother wrote on Facebook. .

Folks at 62nd and Michigan Road. Perhaps 150 here now. pic.twitter.com/5cBOYlkurz

— Robert Scheer (@bobscheer) May 7, 2020

As news of Mr. Reed’s death quickly spread on Wednesday night, another tragedy played out on the South Side of the city, where a pregnant woman was struck by an officer who was driving to work at about 9:45 p.m. The woman, identified by the coroner as 23-year-old Ashlynn Lisby, and her unborn child both died at a hospital, the police said, despite the officer’s efforts to resuscitate her.

Chief Taylor said that a preliminary investigation, which included drawing blood from the officer, Jonathon Henderson, showed no indication that the officer was impaired, and that the woman was struck while she was walking in a lane of traffic on a ramp to a highway.

Then, overnight, four police officers who had driven to an apartment to investigate a burglary report at about 1:30 a.m. instead found themselves confronted outside by a young man with a rifle, who fired at the officers, Chief Taylor said. The officers all returned fire, killing the man, who was identified as McHale Rose, 19.

Chief Taylor said that he did not yet know the motive, but that Mr. Rose may have called 911 to lure officers to the scene “with the intention of initiating an ambush-style attack.”

Chief Taylor said he did not know if the apparent attack was in response to the shooting of Mr. Reed, which took place about three miles away, but said the police were looking into the possibility. No officers were injured in any of the encounters.

The chief also drew the public’s attention to the shouts of distress from the officer who shot Mr. Reed, the audio of which was captured on the Facebook Live video, which he said showed “remorse, sadness, frustration and anguish.” Shortly after the gunshots stop, the officer repeatedly shouts “Oh my God” and utters a series of expletives.