Here's what we know about the police officers who died in the Dallas shootings

Brent Thompson, 43, was a Dallas Area Rapid Transit (DART) officer. He was the first officer in that agency to be killed in the line of duty.

"Brent was a great officer," James Spiller, police chief of DART, told CNN. "He was an outstanding patrol officer as well as a rail officer. We have the highest respect for him."

Brent previously worked for a security firm, and helped train police in Iraq and Afghanistan. Justin Barnes, who served with him, posted a tribute on Facebook:

"Brent was a great man, he was the glue that held us together on many occasions, he kept the peace amongst us, always willing to give you anything he had, always willing to talk and make you feel better. Calm, cool, collected - a true professional."

Two weeks before his death, Brent had married a fellow DART officer. He was also a father and grandfather from a previous marriage.

Michael Krol, 40, had always wanted to be a cop. Eight years before his death, he moved over 1,000 miles away from his home in Michigan to become a Dallas police officer.

“He was a big guy and had a big heart, and he was a really caring person and wanted to help people,” his brother-in law, Brian Schoenbaechler, told the Washington Post. “It doesn’t seem real. His mom’s had a difficult time.”

Previously, Michael had worked as a security guard at a Michigan hospital and in the Wayne County jail system. According to his family, he loved to protect people.

"I had the honor of working with Officer Krol at Division 3 in 2003, Radken Smith, a former colleague, wrote on Facebook. "He was not only a good officer, but a good person."