Police detectives would keep discreet watch at funerals where wanted gangsters are expected to attend. They'd avoid direct confrontation or arrests there and then. They'd keep on the trail and arrest later whoever they want to arrest.
During my father's and uncle's wakes, most gangsters on wanted list came between 4 to 6 a.m., gave white gold paid respects and left a.s.a.p. That's everybody's weakest hours of alertness, including police detectives.
However, if a gangster's unaware that he's wanted and shows up at a police station or court, the police must be blind or mad or simply incompetent and negligent not to arrest him there and then.