Mayor Bill de Blasio observed a moment of silence at City Hall Tuesday afternoon to remember the two officers that were killed in the line of duty Saturday.

The moment of silence was held at 2:47 p.m., marking the exact time that officers Liu and Ramos were ambushed.

"There's a lot of pain right now. We have to work our way through that pain," said de Blasio. "We have to keep working to bring police and community closer together. We have to work for that perfect union."

Meanwhile, police remain on high alert across Long Island and the country, bracing for the possibility of a copycat attack. But investigators believe gunman Ismaaiyl Brinsley acted alone.

Gov. Cuomo, Mayor de Blasio and others have called for restraint after the murders. Mayor de Blasio is also asking that there be a pause in protests about police conduct until officers Liu and Ramos are laid to rest.

A wake will be held for Officer Ramos Friday night at Christ Tabernacle Church in Queens. His funeral will be on Saturday morning.

Arrangements for Officer Liu are pending until his family makes the trip from China.