No one will ever confuse Jim Murray with a teenager. His tall frame, broad shoulders and clipped gray hair give him away for the grandfather he is.Internet child safety experts say police officers like Murray are heroes who do good work at the cost of wading through the muck of online pedophile fantasies.His latest catch was the biggest: four felony enticement charges against a town mayor, who after his arrest called Murray up and begged him to make the case go away....