It's been three years since the Boston Marathon bombing, but for the families who lost loved ones and survivors of the attack, the grieving is not over, says Carlos Arredondo, who was at the finish line on that day.
“Many survivors of the marathon have been grieving along the way, supporting each other,” he says.
The twin bombings killed three people and wounded more than 260. In the aftermath of the attacks, many used the phrase Boston Strong to rally behind the survivors, victims and first responders.
Here's an update on five people who became symbols of strength following the attacks:
Cowboy hat-wearing marathon hero:
Arredondo lost his son Marine Lance Cpl. Alexander Arredondo, during the 20-year-old's second tour of duty in Iraq in 2004. Arredondo was at the Boston Marathon on April 15, 2013, handing out American flags to people who were running on behalf of fallen soldiers. When the blasts went off, Arredondo sprang into action.
Donning a cowboy hat, he ran to the aid of Jeff Bauman, whose legs were blown off by the blast
"I was just trying to look at Jeff in the face and try to comfort him,” he says. “I was just hoping that he would stay awake, kept saying ‘stay with me, stay with me.'"
Since the attack, Arredondo and Bauman have formed a "beautiful friendship." The two were strangers until the attack
"We built a bond, we celebrate holidays together, he supports me in my events and I support him at his events when he has something," Arredondo said in a phone interview. "I am so proud of him."
Since the attack, Arredondo and his wife have launched the Arredondo Foundation. He said the organization provides support to military families that have experienced suicide and provides scholarships for military family members seeking educational assistance.
Four people are running on behalf of the foundation at the Boston Marathon on Monday, April 18.
Jeff Bauman, iconic Boston bombing victim, speaker
Bauman attended the Boston Marathon to cheer on his former girlfriend, Erin Hurley. When the pressure cooker bombs exploded, his legs were blown off below the knee.
The 27-year-old became one of the most recognizable faces of the attacks after a photographer captured an image of him being wheeled to an ambulance by Arredondo and other bystanders. He later identified one of the attackers from his hospital bed.
Today, Bauman travels the country sharing his story and will soon be portrayed by Jake Gyllenhaal in the movie Stronger, which chronicles the Boston Marathon attack.
He says he is still moving on from the tragedy, and admits it is hard to think about what happened.
“Sometimes I have nightmares and wake up to explosions, but it hasn’t been like that for a while. Definitely going over this, it’s tough — it’s a tough subject for everybody,” Bauman told USA TODAY's Andrea Mandell.
Bauman says he looks forward to the 2017 premiere of Stronger, which focuses on the Bostonians, like Arredondo, who gave him the strength to walk again.
"He's one of my best friends," Bauman said of Arredondo.
The Norden brothers
J.P. and Paul Norden were at the Boston Marathon finish line to cheer on their childhood friend when the first explosion went off. As the brothers and their friends tried to make their way to the street and off the sidewalk, the second explosion went off in front of the Forum Restaurant, where they were standing.
"JP, Paul Norden and their friend Marc took the brunt of the explosion," according to the Nordens' Facebook page.
J.P. and Paul, who were both construction workers, each lost a leg.
Since the attacks, the brothers' mom created the non-profit A Leg Forever for her sons, which has raised money to sponsor several people running in the Marathon on Monday.
Survivor running in 2016 Boston Marathon
Professional dancer Adrianne Haslet-Davis attended the marathon as a spectator and was cheering on runners when the bombs went off. Although doctors had to amputate her leg below the knee, Haslet-Davis resolved to dance again.
With the help of a prosthetic leg, she did just that in March of 2014.
On Monday, Haslet-Davis will take on a new challenge: Running the Boston Marathon.
She recently told CBS that running has been one of the biggest challenges she has ever faced.
"Running for me was like torture," Haslet-Davis told CBS. "I mean, I would run a block and be winded and feel like I was going to die."
Boston Marathon bombing survivor killed in car crash
In one of the most heart-wrenching images of the Boston Marathon bombing aftermath, Victoria McGrath, clings to a firefighter as he carries her away from the site of the bombing.
McGrath, who was 20 at the time, was standing near the finish line when a bomb exploded just feet from her.
While recovering in the hospital, McGrath, thanked the firefighter, Jim Plourde, who carried her to safety, and the other first responders who saved her life. In March, McGrath was killed in a car accident while traveling in Dubai, according to a Northeastern University spokesman.
Plourde told the Boston Herald he was "devastated" by McGrath's death.
"After the Boston Marathon bombing, Victoria became a major part of my life as well as my family's," Plourde told the Herald. "It's been said that I helped to save her life, but the truth is Victoria saved my life after the marathon as her love, support and friendship helped myself and my family deal with the acts of 4/15/13."
Contributing: Andrea Mandell
Follow @MaryBowerman on Twitter.