CHICAGO (CBS) — City officials have released additional surveillance video in the Laquan McDonald case, but the video raises more questions than it answers, due to what’s not seen.

Surveillance video from a Burger King near where McDonald was killed has a mysterious 80-minute gap covering the time when McDonald was shot by Officer Jason Van Dyke on a nearby street.

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The video does show officers inside the restaurant after McDonald was shot dead, but the missing footage has prompted allegations of a cover-up by police officers who responded to the fatal shooting.

Lawyers for McDonald’s family have said the Burger King’s cameras likely would not have recorded the shooting itself, but might have filmed McDonald’s movements just before he was killed.

Most of what remains on the videos from Burger King shows officers inside the restaurant after the shooting, and footage of the parking lot, but not the crucial moments when McDonald crossed that parking lot just before his death.

Chicago police and Cook County prosecutors have said there is no evidence of tampering.

“What I can tell you about the Burger King video is that forensic testing on the Burger King surveillance system to determine if anyone tampered with the evidence, and the testing did not reveal any such evidence,” Cook County State’s Attorney Anita Alvarez has said.

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According to published reports, the FBI also has determined there is no evidence of tampering.

However, the regional manager for Burger King has accused police of erasing surveillance video from the restaurant.

Jay Darshane said several police officers were inside the Burger King for at least two hours after McDonald was killed. He said they were given the password to the surveillance camera system, and were left alone in the office as they examined video footage.

Darshane and many protesters have said they believe police purposely erased the video in question.

After McDonald was killed, investigators with the Independent Police Review Authority visited the Burger King to look at their videos, and immediately asked about the gap in the footage. Darshane said he was surprised to learn of the gap, and called in an IT specialist to examine the system.

Darshane said the specialist determined the missing footage had been permanently deleted by someone with “advanced computer skills.”

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Both Darshane and the IT specialist have testified before a grand jury. The computer expert demonstrated how the surveillance system’s logs showed someone had been working on the system just before the video disappeared.