A Folsom Prison tower guard shot an inmate in the arm to stop the man from knifing an inmate from San Bernardino in the exercise yard of the security housing unit, a prison spokesman said. Lt. T.J. Smith said Rex Brownell, 30, serving terms for kidnaping and assault with a deadly weapon convictions in Stanislaus County, was wounded while attacking inmate Gary St. John, 22, who suffered stab Wounds on his left side and near the right eye. Smith said Brownell halted the attack after a guard fired three warning shots, but resumed the assault a few moments later. Brownell was listed in fair condition at a Sacramento hospital. St. John, 22, serving a term for a burglary conviction in San Bernardino County, was treated at the prison infirmary.