(CBS) — A University of Chicago law professor is calling for the release of Chicago Police squad car video of a fatal shooting by officers two months ago.

It was October 20 when 17-year-old Laquan McDonald was armed with a knife and refused to drop it when police surrounded him on the Southwest Side and in fact, he lunged at officers – so they shot him – according to the police account.

Laquan McDonald died of multiple gunshot wounds.

The Independent Police Review Authority is investigating the shooting by officers. IPRA investigations can take many months or years.

In the meantime, U of C Law Professor Craig Futterman says the city of Chicago should release the squad car video from their encounter that night with McDonald because he says a witness tells him McDonald did not lunge at police.

“Far from the young man approaching any officer with a knife. After an officer got out of the car, the kid retreated and tried to shy away toward the fence and that’s when the officer first shot him, and he fell to the ground, dropping the knife.”

Futterman says video of the incident would reveal the truth – whether officers acted properly or improperly.

WBBM is contacting police and IPRA for a response.