At New York's St. Patrick's Cathedral ... a mass ... in memory of two fallen NYPD officers, with Mayor Bill de Blasio and the police commissioner in attendance.
The two officers were ambushed and shot dead ... in what police say was an "execution".
They say the suspect was bent on killing officers as revenge for police shootings of unarmed black men.
Police say he came to Brooklyn from Baltimore, where he had also shot and wounded his girlfriend.
Baltimore's police union president says growing anti-police sentiment has reached crisis levels.
SOUNDBITE: BALTIMORE POLICE UNION PRESIDENT GENE RYAN SAYING:
"Not since the political unrest of the 1960's have police officers been so targeted. And I think it's important to remember that this isn't just a Baltimore or New York problem, this is a powder cage nationwide."
Mayor de Blasio has ordered flags flown at half staff around the city.
But New York's main police union is roundly criticizing hi
