The barrage of gunshots was so loud it cut through the din of Fourth of July fireworks. A man in his 30s, who had been leaning against a parked car with his pregnant girlfriend, fell to the ground, fatally shot in the head.

“I heard about eight shots and came rushing out,’’ said a Dacia Street resident who identified himself as Mr. Gonzalez. “The man was just lying on the ground with a bullet hole in his head.’’

The pregnant woman tried to comfort him, the neighbor said. A boy ran over shouting “They shot my dad!’’ as a car sped away. Police have not identified the victim.

The Dorchester shooting, which happened shortly before 10 p.m. Wednesday, was the second outbreak of gun violence in the neighborhood that evening. Just a few hours earlier, four people were shot, one critically, about a half-mile away on Fayston Street, down the street from a holiday cookout where children were playing in an inflatable bouncy house, police said.

On Thursday, Boston Mayor Martin Walsh condemned the violence and expressed frustration over the lack of cooperation with police in neighborhood shootings.

“I’m not blaming the community for the shootings. What I’m blaming is the people that have guns that are shooting each other,’’ Walsh told reporters on Thursday. “You send a wrong message to children that are in the neighborhood that want to enjoy the fireworks.

“It’s time for the kids who are active in the game, in the neighborhood, to step up, man up, and start to take responsibility for who they are, and never mind this coward way of shooting each other and not telling anybody,’’ he added.

Boston Police Commissioner William Evans said the Fayston Street shooting broke out after an argument at a house party spilled into the street. Three different types of bullet casings were found at the scene, suggesting that multiple people fired weapons, he said.

One of the victims drove away in a car but was stopped within a few blocks and taken to the hospital, police said. Another man went to the hospital himself, and the remaining two were found at the scene.

Wanda Miller, 54, had rented the bouncy house castle for a graduation celebration for her cousin, and said at least 20 children had come to her home to play. She was inside when she heard gunshots, then her cousin’s shriek.

“She was screaming for the kids to get out of the moon bounce, but they weren’t paying her no mind,’’ Miller said. Outside, she saw a man lying in the street and another hiding near her relative’s vehicle.

After the police removed tape from the crime scene, Miller said a relative found a gun under their car and notified police. Officers returned around 10:30 p.m. and said they had established a secure crime scene when a dog “came running from between two parked cars like a missile,’’ said Boston Police Sergeant John Boyle.

Police shot the dog, an 8-year-old pit bull.

The dog’s owner said the animal bolted from her house and that she was trying to call it back.

“I screamed her name, ‘Chyna, stop!’ and her ears perked up and she turned. Then I heard ‘bap, bap, bap,’ ’’ said Shirley Goode, 59.

Homicide detectives are also searching for those responsible for the fatal shooting of a man in Roxbury on Tuesday night. The man, identified by police Thursday evening as Luis Martin Pinales-Perez, 31, of Boston, was fatally wounded near 134 Crawford St., police said.

A neighbor who asked to remain anonymous said Pinales-Perez was among a crowd of neighbors sitting on a front stoop, although he did not live on the street. Not long before midnight, the group thought they heard firecrackers until they saw several men sprinting down the street, firing guns.

People quickly scattered, but Pinales-Perez struggled to get out of his chair. He had been shot in the throat.

No arrests have been made.

Milton Valencia and Felicia Gans of the Globe Staff and Globe correspondent J.D. Capelouto contributed to this report. Jerome Campbell can be reached at jerome.campbell@globe.com or @jeromercampbell. John R. Ellement can be reached at ellement@globe.com.