A 13-year-old boy was found early yesterday morning having apparently killed himself in Marinwood, in San Rafael. He was in an exposed public area along Grande Paseo, and was found by another student walking to school. The cause of death and the student's name have not been revealed, but a school district superintendent insists, "He was a very popular person." The eighth-grader's death follows the suicide of a fifteen-year-old girl from nearby Terra Linda High School last week.