What's Happened So Far in the Boston Marathon Bombing Trial

On April 15, 2013, at approximately 2:49 PM, two pressure cookers filled with shrapnel exploded on Boylston Street, ripping through Boston Marathon spectators and crowds streaming out of Fenway Park after a Red Sox win. Three days later, the FBI's website featured a photo of prime suspect Dzhokhar Tsarnaev, and after a manhunt that included a deadly shootout, the 19-year-old college student was apprehended inside a drydocked boat in Watertown, Massachussetts, on April 19.

Besides Tsarnaev—who went by the nickname Jahar with his UMass Dartmouth peers—police found messages scrawled on the beams of the boat. Among them were, "We Muslims are one body, you hurt one you hurt us all," and, "Stop killing our innocent people and we will stop."

On Wednesday, the trial for the Dzhokhar Tsarnaev began in Boston, and his defense lawyer opened up with the admission: "It was him."

So with the possibility of proving his innocence off the table, the trial—which could last until June—centers on whether Tsarnaev should be put to death or sentenced to life in prison without the possibility of parole.

To that end, the prosecution will argue that the defendant wanted to punish the United States for mistreating Muslims, while the defense will claim that he was merely a tool of his radicalized older brother, Tamerlan.

In his opening arguments, assistant US attorney William Weinreb talked about the three people who died in the attack, including an eight-year-old named Martin Richard, who had no blood left in his body by the time he arrived at the hospital. To highlight the atrocity of Tsarnaev's alleged crimes, Weinreb juxtaposed happy, smiling photos of the deceased with descriptions of their brutal final moments.

Tsarnaev's defense attorney, Judy Clarke, asked the jury to consider the fact that her client was a regular college kid. And, indeed, he was by many accounts typical in the sense that he loved watching the Walking Dead and smoking weed.

He was born in Kyrgyzstan to a Chechen father who wasn't religious. His older brother, according to Rolling Stone, discovered Islam in 2009 after his dreams of becoming a national boxing championship were dashed due to his non-citizen status. Soon he became devout and starting pressuring Dzhokhar to do the same.

"He was in a tough time in adolescence, which we all know, being vulnerable to the influence of his brother," Clarke told the jury. "We ask you to look further."

Keeping with the strategy of bombarding the jury with details of the tragedy, the prosecutor then called several witnesses to the stand to recount their horror, with the hopes that they would eliminate any sympathy the defense might try to engender. Clarke did not cross-examine any of them. On Thursday, more survivors and first responders shared their stories.

Rebekah Gregory, a woman who lost her leg in the bombing, was one of the people who testified Wednesday. Later, she wrote an open letter to Tsarnaev on Facebook about how she used to fear him but now pities him. She mocked the fact that he's sitting in solitary confinement and will either die or do so for the rest of his life.

"So man that really sucks for you bro," she wrote. "I truly hope it was worth it."

Follow Allie Conti on Twitter.