EXCLUSIVE

The mother of Joe McKnight^[1]'s 8-year-old son tells TMZ Sports ... the man who shot the ex-NFL running back is a cold-blooded killer and is begging the court to keep him locked up for LIFE. 

We spoke with Michelle Quick -- who dated Joe back in the day and stayed on close, good terms with him over the years as they co-parented their son, Jaiden. 

In fact, Michelle attended Ronald Gasser^[2]'s trial every day and strongly believes he should have been convicted of 2nd degree murder instead of the lesser charge of manslaughter. 

Gasser is facing up to 40 years^[3] in prison for shooting and killing McKnight in Dec. 2016. The sentencing phase of the case is set for March 15. 

"He never needs to walk the streets ever again," Quick tells us ... "I think the proper sentence is life in prison. He never needs to be out in society."

Gasser is 56-years-old -- so the maximum 40-year sentence would essentially serve a life sentence. 

McKnight's son Jaiden -- with the permission of his mother -- told us he loves and misses his father tremendously and in our video he explains why his dad was the best ever. 

References^ Joe McKnight (www.tmz.com)^ Ronald Gasser (www.tmz.com)^ facing up to 40 years (www.tmz.com)

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