The shooters who killed brothers Jose Martinez, 24, and Samuel Martinez, 20, and critically injured their cousin in Glassell Park early Saturday morning remain at large, police said today. The brothers were walking to their Cypress Park home after going to a store with their cousin, 19-year-old Marvin Gonzalez, when they were confronted by suspects in the 2900 block of Division Street, which serves as a border between two area gangs. The suspects then opened fire, leaving the Martinez brothers with fatal head wounds, said Det. P.J. Morris of the Northeast Division. Their cousin, Gonzales, remains in critical condition. Morris said the the Martinez brothers and Gonzales were not affiliated with a gang.