The Long Island man whose tip proved key to nailing Gilgo Beach murder suspect Rex Heuermann wants to know why it took police more than a decade to follow up on his lead. “I gave them the exact description of the truck and the dude,” David Schaller said in his first interview since the accused serial killer’s arrest July 13. “I mean, come on! Why didn’t they use that?” Schaller, who lived with Gilgo Beach victim Amber Lynn Costello before she disappeared in September 2010, told cops at the time that the man he believed to be her abductor looked...