Geoffrey Fieger said Monday that the video shows police fired into the home at least once after lobbing a flash grenade through a window.
He says that contradicts the police department's explanation that an officer's gun fired during a confrontation with a resident inside the home.
Seven-year-old Aiyana Jones was shot in the neck and died.
Fieger says he viewed three to four minutes of footage but declined to say who showed it to him.
Police are trying to obtain footage from an A&E camera crew that was at the raid.
An A&E spokesman declined to comment.
State police will take over the investigation of the fatal shooting of 7-year-old Jones, a prosecutor said Monday.
Wayne County Prosecutor Kym Worthy said bringing in the state police to investigate the killing would avoid any appearance of a conflict of interest.
"I agree that it is most appropriate that this be done independently," Worthy said.
Aiyana was asleep on the living room sofa in her family's apartment when Detroit police, searching for a homicide suspect, burst in and an officer's gun went off, fatally striking the girl in the neck, family members said.
Her father, 25-year-old Charles Jones, told The Detroit News he had just gone to bed early Sunday after covering his daughter with her favorite blanket when he heard a flash grenade followed by a gunshot. When he rushed into the living room, he said, police forced him to lie on the ground, with his face in his daughter's blood.
"I'll never be the same. That's my only daughter," Jones told WXYZ-TV.
Assistant Chief Ralph Godbee said officers set off the flash grenade as they entered the apartment with their guns drawn about 12:40 a.m. Sunday with a warrant to look for a suspect in the Friday slaying of a 17-year-old boy. The lead officer's gun went off after he encountered a 46-year-old woman inside the front room of the home and "some level of physical contact" ensued. Police do not believe the gun was fired intentionally.
"This is any parent's worst nightmare. It also is any police officer's worst nightmare," Godbee said.
Family members identified the woman as the child's grandmother and Charles Jones' mother, Mertilla Jones, who has said she was not involved in a struggle with the officer. Police later said the officer may have just collided with the woman.
The officer, who police have not publicly identified, was put on paid administrative leave, Godbee said.
"This is a tragedy of unspeakable magnitude to Aiyana's parents, family and all those who loved her," Godbee said. "It is a tragedy we also feel very deeply throughout the ranks of the Detroit Police Department."
Police eventually found the 34-year-old slaying suspect they were looking for during a search of the building, Godbee said.
Charles Jones said he had to wait for hours to find out what happened to his daughter.
"Her blood was everywhere and I was trying to stay calm, but nobody would talk to me. None of them even tried to console me," Jones told The Detroit News.
Godbee would not comment on newspaper reports that neighbors told police there were children in the house and showed them toys in the front yard. The girl's father said three other children besides Aiyana were in the home when the raid happened.
On the porch outside the family's home on Monday, saddened friends and neighbors added candles, stuffed animals and balloons to a growing memorial to Aiyana.
"I don't know them. I came here because I feel it in my spirit. I'm feeling the pain," said Mark Jones, a 39-year-old Detroit father of four who tied three balloons to the porch railing.
Krystal Sanders, Aiyana's aunt, returned to the home with family members on Monday afternoon.
"We want justice, that's all we want," she said, crying. "We want justice."
When asked if police entered the wrong portion of the duplex that features two separate front entrances bearing individual addresses at opposite ends off the worn front porch, she said: "Yes they did. Yes they did."
A news conference was scheduled at 2 p.m. EDT at police headquarters.
Terrance Echols, 28, said he was in the basement of his home, across the street and two doors down from the home, when he heard a "bang."
He ran upstairs, "and I heard people yelling, 'You killed a 7-year-old girl. You killed the girl."'
He said police quickly converged on the house, blocked the street with patrol cars and later had several adults lined up, leaning against the house.
"They were distraught, but the police had them all stretched out outside."
Charles Jones said he was trying not to be angry but wanted the story to be told. He said Aiyana was a lively child who loved to sing and had recently developed an interest in Hannah Montana and the Justin Bieber song "Baby."
"She was just figuring out what she liked, what she wanted to do with her life," her father said. "I want this story to be heard. This was a wrongful death."