Boston Marathon Bombing Trial: Writing on the Boat Wall, Homemade Bombs

ABC News' Aaron Katersky on the latest testimony from FBI experts in the federal terrorism case against Dzhokhar Tsarnaev.
9:55 | 03/11/15

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Transcript for Boston Marathon Bombing Trial: Writing on the Boat Wall, Homemade Bombs
The writing on the wall jurors saying for the first time these lights streak and bullet hole written messages. Hand written by Joseph cars are ignited inside that boat those notes. Scribbled during an intense standoff with police and Watertown moments for for a five day manhunt came to an end. Nearly two years ago hello I'm tired Hernandez in New York in the Boston Marathon bombing trial prosecutors now calling FBI experts to the stand. Following this trap and inside the courtroom. ABC's Aaron could turn ski hello Aaron at tell us a little bit about court so far this morning. Well we've been hearing from FBI agents who talked about all of the bomb fragments the human remains even that shattered pieces of backpack that were recovered from Boylston street. Some of them plucked from the ground covered in blood. Talks on what it is nearby and all of these worked catalog and and we saw some of them and so the jury for the first time today. Has seen actual pieces of the bomb that was used to cause so much carnage in front of the forum restaurant the second explosion. And these pieces included. Tatters of a backpack. The pressure cooker that was filled with a explosive powder taken from ordinary fireworks the prosecutors said along with BBs and nails. The jury saw pieces of that shrapnel to had been stored in the cannon. An FBI agent put on white gloves and use scissors to pry open neck and plastic bag inside Russell against the microphone made a lot of noise but ultimately the jury got to see. The explosive device that did so much damage. A lot of showings help for that jury talk to us about. The boat big piece of evidence that we haven't seen indeed tail before the message. That Joseph Carr wrote in that boat. Almost tantamount to a confession or are implying. And definitely act and responsibility in some of this but yet the defense. Also on board with showing this to the jury. Well they did this represented the first time that they've been message that Joseph hearts our knives scrawled in pencil while he was hiding from police in the slip away to the seventeen foot boat stored in a backyard in Watertown. Had been showed in its entirety a complete form the complete transcript the panels of the boat where that writing. Was in and it was remarkably flexible given that Joseph hearts are nigh of had been I almost killed by all the bullets that had been fired in his direction. And that's what the jury of what the defense wants the jury to see they want the entire boat visible. So that the jury can see the 200 or so bullet holes all of it the defense established from incoming police fire. Concern I have was on arms despite fears that he might booby trapped the boat it was in fact that a Boston Police bomb technician. That first noticed the note when he swept the vote for explosives after Sinai of had been taken out and he pointed concern I have. Right in court to affirm that that was the guy he saw being taken into custody by the Massachusetts state police. The note itself is expected to be showed we're just waiting for the judge to decide whether will be the panels to the boat in its entirety the judge went to have a look at the boat in storage at an undisclosed location before he makes a ruling. Okay what did the notes say. The note does as you point out tie amount to what prosecutors considered to be a confession. He says that it's part of God's plan for him to hide in the boat. And explain the actions of him and his brother he talked about how his brother had gone off toward martyrdom toward paradise but that he was left to explain himself. He said the killing of the innocent civilians is forbidden in Islam but then he justified. The attack because he said that the US had killed innocent Muslim civilians and he talked about the Muslim nation rising up as one. To prosecutors it's a confession to the defense it was something he wrote under duress because of all the bullets that were fired his way. Seen in the note he was eager to talk about what he did that and give reasons for his actions but this is about as close as we're gonna get hearing directly from our high up her act. They may be unless he's somehow takes the stand during the penalty phase of the case which is not entirely out of the question unlikely though it may be. But remember the defense's central point here it is to spare his life not to acquit him. And their argument their main argument is that he was led down a path that had been paved by his older brother Camarillo and who else can they call but Joseph hearts are and I have to affirm that for the jury Woolsey they also tried to suggest that he's not. The monster. Prosecutors portrayed him as he didn't. Tweets that they showed that the jury prosecutors were very selective they took 45 of the more than a thousand tweets that certain I've had posted. And the defense suggested that had you seen the full scope of this Twitter account. They would have been things about girls and sleet and homework and other typical college kid type stuff. Okay a little bit about what some of the evidence you mentioned earlier. Twisted metal. A lot of objects that really show the violence and all. These explosions were designed to be deadly prosecutors said and they were particularly insidious because of all the shrapnel inside. Meant to take care collects. And cause violent painful death. And prosecutors tried to show jury evidence of that with these BP's with the nails that there was a zipper. In that evidence and that the FBI agents showed the jury and issue is prying open these cans and unveiling their contents. Jurors got to see the bombs in question prosecutors have said they were. Made to the specifications of al-Qaeda from a recipe that was published in inspire magazine. And that's our knives we've we will learn. Made up research that that bomb making recipe online prosecutors have yet to get to that but we expect to hear that a bit later. And they want to show the jury just how awful this was. While prosecutors still have the chance they want to make Jill hearts are nigh of look like someone who was they said as murder in his heart. And so they're trying to do that with his tweets we've the evidence collected from the street. Showing gory images of a blood running through Boylston street and and maimed bodies and human life. And all the while that offensive is trying to implored the jury to hold off. Ask yourself why. And there's not a whole lot they can do. To detoxify some of this evidence tie but they're doing the best they can. Trying to say that that it is tweets were rather innocuous if you look a bit deeper at a rap lyrics that they're quoting. Trying to save it look at all those bullet holes and and and the stress that he must have been under. Unclear how the jury is taking this all in. We've heard a lot from victims people directly affected by those bombings what about the and might keep police officer killed during the five game now. Some of the police officers have testified here and we're gonna hear about more of them for more than because that they were involved. In the investigation of the death of Sean call your BM IT campus police officer. It was the fourth death associated with the marathon plot. And right now and FBI agent has been taking the jury through the movements. Of of Phil harder contaminants are nine at in the days after the bombing he's been doing it through phone records in on the night of April 18 2013. Shows that they were on the move and late at night and what were they doing. Well the prosecutors have said that they were in search of another gun they want of another gun. And when they came upon Sean call yours police cruiser near their home in Cambridge. That's when prosecutors have said they tried to tear open the door and tried to reach for employers gun. Employer was shot at point blank range six times and there is surveillance video of that and counter that the jury is going to see and they're going to hear from a witness. Who said he saw the whole thing unfold. And they are also going to hear. From members of the police departments in Cambridge and at MIT that ended up investigating the scene. A call your died a violent death. And then there was the shoot out between. Police in Watertown Massachusetts. And that's an I have Brothers where contaminants are Knight was killed and and shall hearts and I have. Drove away and that a running over his brother all of that is yet to come. You've just. Rags. Joseph cars it's our and I adds. As emotionless during much of the testimony so far has that still held. It still seems to me that he as a flat to meaner it's so hard to know if he is moved by any of this testimony. It if nearly two years after he dropped that backpack at the feet of cheering spectators he was. Interested in and seeing the tattered remnants of it again. He came to court today looking a little bit different he wore a blue V neck T shirt beneath his dark suit jacket no more collared shirt. He appeared in Iraq a little bit but this lawyers say even joking with them it's seen before the jury came in but during the testimony. He he does not appear to betray any particular emotion. Well much more to come in this trial and he's Aaron Terry thank you so much for joining us. From Boston. And he can keep up with this story in real time by downloading the ABC news happened starring this story for exclusive updates on the ago. Anti Hernandez in New York.

This transcript has been automatically generated and may not be 100% accurate.

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