Presidential candidates Republican Donald Trump and Democrat Hillary Clinton canceled planned events on Friday (July 8) following a deadly mass shooting in Texas that left five police officers dead.

At least one sniper killed five Dallas police officers and wounded another seven in a racially charged attack that ended when police used a robot carrying a bomb to kill him, the city’s shaken police chief said.

The incident began on Thursday evening at the end of a protest over this week’s killing of two black men by local police in the United States.

“I mourn for the officers shot while doing their sacred duty to protect peaceful protesters, for their families & all who serve with them,” Clinton tweeted.

Trump wrote, “Prayers and condolences to all of the families who are so thoroughly devastated by the horrors we are all watching take place in our country.”

Meanwhile, police briefly ordered a lockdown of the U.S. Capitol because of police activity on Friday, and a Senate aide said officers were searching for a woman who may have a weapon in a basement area near the U.S. House of Representatives.

Police gave an all-clear notice to reopen the Capitol building shortly after 9:30 a.m. (1330 GMT), about a half an hour after the lockdown began. It was not immediately clear whether the police had found the person they were seeking.