A 35-year-old man is facing an indeterminate sentence in prison after pleading guilty to murdering a cyclist in Mount Vernon last year. On Monday, Westchester County District Attorney Anthony Scarpino announced that Bobby Jackson of Manhattan pleaded guilty to charges of second-degree murder, criminal possession of a weapon and reckless endangerment for his role in a shooting near the intersection of Third Street and Second Avenue that took the life of a 42-year-old man last April.