The 9-year-old was stabbed to death just minutes after leaving his home by a killer who has never been caught. — Eric Coy loved to ride his bicycle. The 9-year-old, who lived in Martinez, California, spent most of his free time on his BMX bike. On the morning of Saturday, January 24, 1987, he asked his father, Dan Coy, if he could ride his bike to his aunt’s home several blocks…