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'Too soon to say goodbye': Thousands mourn four Houston firefighters

David J. Phillip / AP

Houston Fire Department Chief Terry Garrison, right, presents a flag to the parents of fallen firefighter Anne Sullivan, Mary, left, and Jack Sullivan, during a memorial service for fallen Houston firefighters Wednesday in Houston.

Thousands of first-responders gathered in Houston on Wednesday for an emotional tribute to four firefighters killed in a deadly blaze last week.

Grief, memories and solidarity marked an emotional tribute to the Houston firefighters killed battling a deadly motel blaze. NBC's Janet Shamlian reports.

Texas Gov. Rick Perry, Houston Mayor Annise Parker and 15,000 mourners assembled in Reliant Stadium to praise the heroism of victims Robert Bebee, Matthew Renaud, Anne Sullivan and Robert Garner, who died Friday -- the deadliest day in the Houston First Department's 118-year history. Thirteen other firefighters were injured.

Victims' families entered the memorial as firefighters stood and saluted them. Pictures of the fallen men and women were displayed on screens throughout the stadium, which is the home to the NFL's Houston Texans.

"When the Mayday sounded last Friday here in Houston, I truly believe our members left this earthly place and immediately stood at attention on the row call in Heaven," said Houston Fire Chief Terry Garrison.

After his remarks, Garrison knelt in front of each of the families and presented them with a flag.

Along with the thousands of first-responders in attendance, thousands more around Texas and the country watched the service remotely. Firefighters from the Dallas Fire Department and across the state helped back-fill in Houston as colleagues of the four attended the service, The Houston Chronicle reported.

"These are hard days. It is a painful day. But it's also a necessary day. It is our duty to honor these four individuals represented here. Four people who sacrificed everything in the service of their community," said Perry.

Following the Texas governor, representatives from each of the families delivered moving tributes to their loved ones.

Nicole Garner, sister to Robert Garner, said just weeks before he died that her brother told her that being a firefighter was what he needed to do with his life. "My brother died fulfilling his dream," she said.

Investigators are still trying to determine what caused the fatal blaze at a motel in Houston. When first-responders attempted to rescue motel guests, the building collapsed on them and they became trapped, fire department officials said.

"It is always too soon to say gooodbye to another fallen hero. It breaks our hearts to say goodbye to four," said Parker. "The oath that they and all firefighters swear isn't to come when it's convenient, isn't to come when it's safe; it is to come and serve."

The Associated Press contributed to this article.