Former Monterey Park police officer Kenneth Vest, 25, was convicted in Los Angeles Municipal Court of brandishing a firearm on the San Bernardino Freeway and filing a false report in connection with the March, 1985, episode. Another ex-officer, Rafael Mercado, also 25, was convicted of the false report charge but was acquitted on the firearm count. Both men, who were off duty at the time, were accused of displaying guns after a verbal confrontation with four occupants of a car on the freeway near West Covina. But Deputy Dist. Atty. Thomas A. Gray said trial evidence showed that by the time Mercado reached for his gun and fired at the other car, "he had every reason to believe there was a gun in the other car." After the incident, in which no one was injured, the officers lied about how the fracas had occurred, Gray said. Sentencing was set for Feb. 6.