NEW YORK - Thousands of police and other mourners were expected to fill a New York City church and surrounding streets for the funeral Saturday of one of two police officers ambushed by a gunman who said he was avenging the killing of unarmed black men by police.US Vice President Joe Biden is due to make remarks at the service for Rafael Ramos, whose death, alongside his partner Wenjian Liu, has become a rallying point for police and their supporters around the country, beleaguered by months of street rallies by protesters who say police practices are marked by racism."This is probably going to be the largest one, maybe in the history of the police department," Stephen Davis, the department's chief spokesman, said of the funeral, which is drawing delegations from police forces across the United States."If nothing else it's the way this was done," Davis said in explaining the outpouring of support, "an out and out calculated assassination, even notwithstanding the current controversy, the protests across the country."The service at Christ Tabernacle Church in Ramos's Queens neighborhood will also bring together Mayor Bill de Blasio and the police officers and union leaders for the first time in public since an extraordinary confrontation a week ago at the hospital where Ramos and Liu were pronounced dead.Hours after Ramos, 40, and Liu, 32, were slain while sitting in their parked patrol car in Brooklyn last Saturday afternoon, police officers, in an unusually pointed display of disgust, turned their backs to the mayor as he arrived at the hospital.Marking the most toxic relations in decades between a New York City mayor and his police department, union leaders, enraged by his expressions of support for the protesters, said the mayor had "blood on his hands."The officers' killer, Ismaaiyl Brinsley, 28, fatally shot himself soon after the attack, and had earlier shot and wounded his ex-girlfriend in Baltimore that morning.