The mother of Joe McKnight'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's trial every day and strongly believes he should have been convicted of 2nd degree murder instead of the lesser charge of manslaughter.