Mayor Bill de Blasio, publicly silent and largely out of view the day after two police officers were killed in Brooklyn, re-emerged on Monday, straining to demonstrate leadership over a fractured city.

Mr. de Blasio visited the families of the slain officers, spoke to a nonprofit police group and, for the first time since the shooting, took several questions at a news conference at Police Headquarters.

And at every stop, the Democratic mayor of New York, who ascended to office with a pledge to reshape the Police Department, had company: Police Commissioner William J. Bratton — once renowned for helping turn back crime in the 1990s, now the essential bridge between the mayor and a department that distrusts him more deeply than ever.

Mr. de Blasio, at the helm of a city still raw from weeks of protests after a grand jury’s decision, called for a suspension of the demonstrations, asked the public to report any possible threats against police officers and urged New Yorkers to thank and console officers in mourning, even as detectives continued to trace the movements and communications of the gunman before the attack on Saturday.