For Detective John Walcott, the trouble began in the spring of 2003.
For "some crazy reason I was feeling sluggish," he said, but he dismissed it, thinking he was just "exhausted from the long season" he'd spent coaching a high school varsity hockey team that he'd led to a sectional championship.
"I just didn't feel right," he said to ABC News.
He was diagnosed with acute myelogenous leukemia (AML) and was told that without a bone marrow transplant he would die.
A hematologist friend of Walcott's told him grimly, "I'm not going to lie to you. You're going to go in for the most painful experience of your life. They're going to stick this, like, 5-foot needle down your spine, take a fish hook, and carve your bone marrow out."
Walcott, a detective from one of the most crime-ridden precincts in the Bronx, passed out from the pain.
He spent a month in the hospital and then came home to his family in Pomona, N.Y.
But he was too susceptible to infection to leave the house.
He said his daughter couldn't go to birthday parties or play dates, and he couldn't leave his house.
Coaching the hockey team again was completely out of the question.
"If you had a cold or even allergies, you couldn't come over to my house. … At Christmastime my uncle had a cold and he couldn't come over," Walcott said. "Turned out he passed away [the following] May."
Walcott said he was approaching his 40th month in remission.
Like hundreds of police and firefighters who responded to the call for help on Sept. 11, Walcott believes his cancer is related to his work on "the Pile," as ground zero is known to the men and women who volunteered there.
He is part of a class-action lawsuit alleging that the city, state and federal government did not adequately protect ground zero workers.
He at times became concerned that he sounded like he was complaining. He said his biggest regret was the toll his leukemia had taken on his young daughter.
"She's had a crummy childhood. There's no way around it," he said.
Like his partner of 12 years, Detective Richard Volpe, Walcott responded immediately, on his day off, to the World Trade Center, and got right to work without a mask.
"I got a mask about three weeks later," he said. "And, um, it's kind of funny because you got it, and then one day you went to roll call down there. … Where they give you your assignment for the day. And they said, 'Wait. Before you guys get out to the street for your post, you gotta go to … change the filters on your masks.'"
"We [asked,] 'Why?' and they [said,] 'Well, the ones you had for the last couple of weeks were the wrong filters. They were hurting you more than helping you.'"
"And we went and changed them."
At nights, Walcott went home to eat, sleep and clean up.
"My shower looked like you just paved a driveway black," Walcott said. "And your pillow would be black and your sheets would be black and … your tear ducts in the morning dripping down your face and it was just streaks of black."
"And it was kind of scary because on 9/11, they said, 'Look, no one [can] leave this place until you're all cleaned up. It's dangerous.'"
"So they [would] put you on a bus and -- I'll never forget it -- they took us to, I believe, to a Pathmark [supermarket] and we got off the bus and it was [after] a 15-hour day and you were tired and cold and you knew friends of yours were trapped. … [We were told,] 'Well, we're all out of stuff to clean you up so go home.'"
"And we were like, 'You're kidding us, right?'"
"And they [said,] 'Nope. Go home.'"
Walcott's anger has gone into remission. He said he felt deeply frustrated with the City of New York.
"I thought they were watching out for me," he said. "And I don't agree with a lot of things that the government or the city does, but I would hope that they would take into consideration that after the worst disaster in the world, that they would look after people that were trying to help the country."
With additional reporting by Jennifer Wlach, "Good Morning America"