Boston Marathon bombings survivor Rebekah Gregory in her wheelchair after crossing the finish line of the Boston Marathon Tribute Run with Tracy Kiss, left, in Boston on April 19, 2014. (Elise Amendola/AP)

Boston Marathon bombing survivor Rebekah Gregory has most certainly faced her greatest fears in the past two years.

In spring 2013, a pressure-cooker bomb blew her into the air near the finish line on Boylston Street. When she landed, she said, her leg bones were lying next to her on the sidewalk. She had an amputation. She learned to walk with a prosthetic limb. She got married, and then separated. But hours after she testified in the nation’s most-watched trial on Wednesday, face-to-face with alleged bomber Dzhokhar Tsarnaev, she said she had a realization — and she wrote about it in an open letter to the man whose own lawyer admitted: “It was him.”

Gregory shared the letter Wednesday night on her Facebook page.

“Today I looked at you right in the face,” she wrote, “and realized I wasn’t afraid anymore. And today I realized that sitting across from you was somehow the crazy kind of step forward that I needed all along.”

A courtroom sketch shows Boston Marathon bombing survivor Rebekah Gregory testifying in the trial of accused bomber Dzhokhar Tsarnaev at the federal courthouse in Boston. (Jane Flavell Collins for Reuters)

When two bombs exploded on April 15, 2013, Gregory was watching the race. Her son Noah, who was 5 at the time, was pretending to be a scientist, hunting for rocks, she told jurors, CNN reported. One moment, he was sitting on her feet; the next, she was lying on the ground and her son was nowhere to be found.

“My first instinct as a mother was where in the world was my baby, where was my son,” she told jurors. She scanned the crowd. Then she heard his voice, crying, “Mommy, Mommy, Mommy.” She tried to sit up, but she couldn’t move.

“My bones were literally lying next to me on the sidewalk,” she said. “I thought that was the day I would die.”

“I said a prayer,” she added. “I said, ‘God, if this is it, take me, but let me know that Noah is okay.’ ”

Finally, someone picked up the boy and put him down next to his mother, according to the Associated Press.

In the next 18 months, she had 17 surgeries. In November, she decided to have her lower left leg amputated.

Three people were killed in the marathon bombing. More than 260 were injured. On Wednesday, jurors looked at photos of victims and heard testimony from some who survived it. But jurors weren’t asked to consider whether 21-year-old Tsarnaev was innocent of his part in the bombing. His defense team conceded that he did it, but that he did it naively — a mere youth influenced by his older brother, Tamerlan Tsarnaev, 26, who was killed days later in a shootout with police. It appears to be his attorney’s hope that this could spare him from the death penalty.

Tsarnaev faces a total of 30 charges — 17 of which could carry the death penalty.

“The evidence will not establish and we will not argue that Tamerlan put a gun to Dzhokhar’s head,” his attorney said, “or that he forced him to join in the plan. But you will hear evidence about the kind of influence that this older brother had.”

In this courtroom sketch, attorney William Weinreb, left, delivers opening statements in front of U.S. District Judge George O’Toole Jr., right rear, on the first day of the federal death penalty trial of Boston Marathon bombing suspect Dzhokhar Tsarnaev, seated second from right. (Jane Flavell Collins for AP)

On Wednesday, Gregory walked into the Boston courtroom to take the witness stand in Tsarnaev’s trial. She said in her letter that her palms were sweating. When the prosecutor questioned her, she started crying. But now, she wrote to Tsarnaev, she is no longer afraid. “In so many ways, you saved my life,” she wrote.

“Over the last two years, I have seen your face not only in pictures, but in almost every one of my nightmares,” she wrote. “You have undoubtedly been my source of fear since April 15th, 2013. (After all, you are one of the men responsible for nearly taking my child, and for the permanent image embedded in my brain of watching someone die.) Up until now, I have been truly scared of you and because of this, fearful of everything else people might be capable of.

“But today, all that changed. Because this afternoon, I got to walk into a courtroom and take my place at the witness stand, just a few feet away from where you were sitting. (I was WALKING. Did you get that?) And today I explained all the horrific details, of how you changed my life, to the people that literally hold YOURS in their hands. That’s a little scary right? And this afternoon before going in, I’m not going to palms were sweaty. And sitting up there talking to the prosecution did make me cry. But today, do you know what else happened? TODAY … I looked at you right in the face … and realized I wasn’t afraid anymore. And today I realized that sitting across from you was somehow the crazy kind of step forward that I needed all along.

“And I think that’s the ironic thing that happens when someone intends something for evil. Because somehow, some way, it always ends up good. But you are a coward. A little boy who wouldn’t even look me in the eyes to see that. Because you can’t handle the fact that what you tried to destroy, you only made stronger. And if your eyes would’ve met mine for just one second, you would’ve also seen that what you ‘blew up’ really did BLOW UP. Because now you have given me (and the other survivors) a tremendous platform to help others, and essentially do our parts in changing the world for the better.

“So yes … you did take a part of me. Congratulations you now have a leg up … literally. But in so many ways, you saved my life. Because now, I am so much more appreciative of every new day I am given. And now, I get to hug my son even tighter than before, blessed that he is THRIVING, despite everything that has happened.

“So now … while you are sitting in solitary confinement, (awaiting the verdict on your life), I will be actually ENJOYING everything this beautiful world has to offer. And guess what else? I will do so without fear … of YOU. Because now to me you’re a nobody, and it is official that you have lost. So man that really sucks for you bro. I truly hope it was worth it.

“Sincerely,” she signed, “someone you shouldn’t have messed with.”

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