President Barack Obama and his predecessor, former President George W. Bush, on Tuesday will lead the nation in a memorial service mourning the deaths of five Dallas police officers at the hands of a sniper who used a Black Lives Matter protest to launch an ambush on law enforcement.

The current and former presidents will speak at the Dallas event, joined by numerous state and local officials.

Lone gunman Micah Xavier Johnson, 25, opened fire on officers Thursday night, striking 11 of them: 10 Dallas Police Department officers and one from the Dallas Area Rapid Transit Authority.

Hundreds gathered in downtown Dallas that night — as did many more in other major American cities — to protest the deaths of two black men killed by police officers. Police fatally shot Alton Sterling in Louisiana and Philando Castile in Minnesota last week. Their deaths sparked national outcry about black individuals dying at the hands of law enforcement.

Following their deaths, Obama addressed the nation Thursday, saying there are racial disparities in police shootings but recognizing that the incidents do not contradict the appreciation communities have for most law enforcement.

Hours later, Dallas happened.

State officials reacted via social media and updated followers with each development. Gov. Greg Abbott extended thoughts and prayers and offered state assistance to Dallas. The governor Monday announced his wife, Cecilia, would attend the memorial while he recovers from an infection after suffering severe burns to his legs and feet.