Many political observers saw the ousting of former campaign manager Corey Lewandowski as signaling a new, more professional era for the campaign of 2016 Republican presumptive presidential nominee Donald Trump.
"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", read the tweet. The video statement marked the first time that Trump had publicly named the victims in the shootings.
The deadly shootings in Dallas also left seven officers wounded.
In a CNN interview Friday afternoon, Clinton described the rapid succession of violent events this week - including the videotaped killings of young black men by police officers in Minnesota and Louisiana - as "deeply troubling and it should worry every single American". She didn't mention any of the three shootings (Louisiana, Minnesota, and Texas) by name in that initial conversation.
Trump also addressed the racial divide in the country, saying that tensions have gotten worse.
He doesn't suggest that anti-police rhetoric could have caused such violence, as he has before.
Ms Clinton told the convention Alton Sterling and Philando Castile's deaths are the latest in a "painful litany" of 123 African Americans killed in police incidents so far this year.
Donald Trump's campaign chair in Virginia said Democrats who label police as racist are encouraging attacks like the one in Dallas.
She also spoke sympathetically of the police officers who were killed and their families "who lived every day with the fear that something like this would happen and will always be proud of their service and sacrifice".
Clinton said that as president, she would reduce what she said was "excessive violence" as well as reforming sentencing laws and toughening gun control.
Early Friday morning, before much information was known about the attackers who killed five police officers in Dallas, Trump released a statement about the need to "restore law and order", which was balanced by the implication that something must be done about the use of lethal force by police.
"As a result, today we are seeing one of the noblest professions condemned by those who could benefit the most", he said in statement about the shootings.
Clinton had been planning on delivering remarks about the Castile and Sterling shootings - which have sparked protests across the country - while campaigning alongside Vice President Joe Biden in his hometown of Scranton, Penn., Friday, but that event has been postponed following the police shootings in Dallas. While GOP officials are often seen as siding with the police in recent altercations with black men, some high profile Republicans were pointed Friday in acknowledging racial disparities in policing.
Trump canceled a speech in Miami on Hispanic issues. "I think we've reached a point in the campaign where he's been asked to help and he's helping".
Democratic strategist Bud Jackson said she is hitting the right tone.