Boston Marathon bombing survivor Rebekah Gregory has written about the emotional experience of testifying in the trial of defendant Dzhokhar Tsarnaev, which began Wednesday in Boston. Above, Gregory (second from right) crossed the marathon finish line during a Tribute Run for survivors and first responders in Boston on April 19, 2014. Reuters/Brian Snyder

Testifying in the trial of Dzhokhar Tsarnaev left Boston Marathon bombing survivor Rebekah Gregory with a flurry of powerful emotions. She shared them in a public Facebook post Friday.

"I am in such awe of my fellow survivor's [sic] bravery, who have and will testify in the ... coming weeks," Gregory wrote. "And I am amazed at our country as a whole, supporting us in every step since the beginning."

Gregory ultimately lost much of her left leg after enduring nearly 20 surgeries as a result of the April 2013 bombings. "It's bittersweet to be leaving Boston today," she also wrote. "Although this place is the source of so many painful memories, it also feels like my second home." The post had nearly 4,000 likes by noon Friday.

For Gregory, who is from Houston, the trial was the first time she had seen Tsarnaev, who is accused of carrying out the bombings that killed three people and injured more than 260 people. Afterward, she wrote a long letter, posted to Facebook on Wednesday, calling the defendant a coward and sharing how she had changed and grown since the bombings.

"You have undoubtedly been my source of fear since April 15th, 2013," she wrote. "But today, all that changed."

In court Wednesday, Gregory shared how she had tried to help her 5-year-old son, who survived, after the bombs went off, but could not. "My bones were lying next to me on the sidewalk," she said. "At that point I felt that was the day I would die."

Others who testified this week included Bill Richard, whose 8-year-old son Martin was killed in the bombings and whose 7-year-old daughter lost one of her legs. Boston police officers also testified, as did other survivors of the bombings.

Dzhokhar Tsarnaev faces 30 charges related to the bombings, including conspiring with his brother Tamerlan, who was killed in a firefight with police a few days after the bombings. He faces either life in prison or the death penalty.