BOSTON — Construction of a memorial that honors the victims of the 2013 Boston Marathon bombing is nearing completion.

Workers have installed four bronze columns at both explosion sites along the marathon route, symbolizing the lives the Tsarnaev brothers stole in the attack – Martin Richard, 8, Lu Lingzi, 23, Krystle Campbell, 29 – in addition to MIT campus police officer Sean Collier, 26, who one of the brothers later shot after stealing his gun.

BOSTON MARATHON RUNNERS BRAVE STRONG WIND, RAIN FIVE YEARS AFTER BOMBING

The memorial's columns encapsulate glass spheres that will emit light, artist Pablo Eduardo said.

“It symbolizes the way we protect our ideas," Eduardo said. "How we cherish things that are very fragile.”

Carlos Arredondo, dubbed "the hero in the cowboy hat," said returning to the finish line has gradually gotten easier with time.

BOSTON MARATHON BOMBER’S LAWYERS WANT DEATH SENTENCE TOSSED, ARGUE IT’S IMPOSSIBLE FOR HIM TO GET FAIR TRIAL IN CITY

"It's a healing process," Arredondo said. "I just hope people will understand the meaning behind this memorial."

Right before the blast in 2013, Arredondo was handing out American flags to runners crossing the finish line. Moments after the first pressure cooker detonated, he sprang into action, lept over a fence and extinguished the flames from a man who had just lost both of his legs.

Arredondo was there that day handing out the flags in honor of his two sons – U.S. Marine Lance Cpl. Alex Arredondo, who was killed in Iraq in 2004, and his brother Brian who committed suicide in 2011. He recalls at the end of the day pulling from his back packet a blood-soaked American flag, something he cherishes to this day.

Since the attack, he has launched an organization with his wife Malida to provide assistance to families of service members who commit suicide. He said what he witnessed that day has shed light on what service members often go through, informing his work with the foundation.

Last year, he ran in the race for the very first time.

"The scars, you know, PTSD, flashbacks, many of us are still going through that," Arredondo said, adding that the new memorial will help the healing process. "The families can continue grieving and we're here to also grieve along with them."

In addition to the four columns at both sites, three granite monuments engraved with poetry will also mark where the three blast victims died. The planning process took more than four years, $2 million, and at the request of the victims' families, a complete redesign to reflect their input, WBZ-TV reported.

CLICK HERE TO GET THE FOX NEWS APP

Arredondo, who immigrated from Costa Rica in 1980, said people still stop him on the street and thank him, especially when he's donning his cowboy hat. He insists though, that he did that day what any true Bostonian would do.

"They might call me a hero, and I say 'thank you very much,' but that's how we are in Boston," he said. "It's a wonderful legacy here."

The city expects the electrical work to wrap up on the columns over the next few days.