DALLAS (CBSDFW.COM) — Today marks five years since one of the saddest days in Dallas history — when five officers were ambushed, shot and killed while working downtown.

Gunfire from a lone gunman led to the chaos that sent officers scrambling to secure the scene and activists participating in a peaceful protest running for cover. It was the deadliest attack on police since 9/11.

Dallas Police 7/7 Ambush victims — DART officer Brent Thompson and Dallas police officers Lorne Ahrens, Patrick Zamarripa, Michael Krol and Michael Smith. (credit: CBS 11 News)

The evening of July 7, 2016 started uneventful as demonstrators marched through downtown Dallas demanding justice in two police involved shootings in Louisiana and Minnesota. But the night ended with five police officers shot and killed.

The ambush took the life of Officer Patrick Zamarripa. The 32-year-old Fort Worth native was a loving father. He was also a Navy veteran who survived three tours during the Iraq War.

Officer Michael Krol was a Michigan native who dreamed of serving and protecting in Dallas. After working as a security guard and a corrections officer, the 40-year-old was a member of DPD for eight years.

Sr. Cpl. Lorne Ahrens, a former semi-pro football player, served with the Dallas Police Department for 14 years. Loved ones said he had a crooked smile and a wicked sense of humor. He was a father of two and husband to a fellow police officer.

Sgt. Michael Smith was also the father of two kids. Family said the 55-year-old died doing what he loved. He was a former Army Ranger, and at the time of his death had been married for 17 years.

Officer Brent Thompson is the first DART officer to die in the line of duty. The 43-year-old officer had just married a fellow transit officer two weeks before the shooting. Thompson also left behind six children.

A memorial service being held today will begin with a short march to the Dallas Police Memorial site. There will be a performance from the Dallas Police Choir, remarks from Dallas Police Chief Eddie Garcia, a fly over, and a “Roll Call of Honor.”