New surveillance footage of a Boston bomber laying an explosive then fleeing the scene has been shown in court. Footage shows Dzhokhar Tsarnaev walking through the city before pausing near the finish line, where he dropped an explosive charge that killed an eight-year-old boy. He is seen standing in the crowd for several minutes, before calling his brother, Tamerlan. Shortly after the call, the first bomb explodes - at which point he pushes his way through the stunned crowd. Tsarnaev managed to clear the blast zone in the 12 seconds between the first bomb exploding and his going off - but is still in the shot from a surveillance camera at the scene. Shock: Dzhokhar Tsarnaev, cirlced top left, is pictured above in FBI surveillance video standing in a crowd the moment the first bomb goes off at the Boston marathon. While most of the crowd looks towards the blast, he heads off in the other direction . Explosion: Pictured above is the moment Tsarnaev's pressure cooker bomb exploded. It killed two people and wounded dozens more . Killer: The blast ended the life of 8-year-old Martin Richard, and also robbed his sister of one of her legs . Some 12 seconds later, a second explosion takes place precisely where he was standing. He is later shown running from the scene without the backpack he was carrying earlier. It is unclear exactly how the bomb was detonated - though early claims that it primitive kitchen-timer device seem to be endorsed by the fact that Tsarnaev was still fleeing when the bomb went off. The blast killed eight-year-old Martin Richard, as well as Lingzi Lu, a 23-year-old student. Martin's younger sister, Jane, lost a leg in the blast and hundreds were injured. The footage was shown to jurors weighing up whether to sentence Tsarnaev to death for the bombing - which his lawyers do not deny he did. The video - nine and a half minutes in total - was compiled by FBI investigators from surveillance footage around the city. Plotting: Dzhokhar, circled in white, is pictured here before the blasts. His brother Tamerlan Tsarnaev, who was killed in a gun battle days later, is circled in black . It shows both brothers walking the streets before splitting up to set down the pressure cooker bombs near the finish line on April 15, 2013. He is the only surviving bomber, as Tamerlan Tsarnaev was killed in a gun battle days after the attacks. Defense attorneys have argued that Tamerlan persuaded his brother to carry out the attacks, and as such he is not as culpable. Seconds later, the second bomb explodes, and Tsarnaev, who prosecutors say detonated the second bomb, is seen running with a crowd of people who also are running, pushing some out of his way to flee the scene. People are also shown jumping over metal barriers as smoke wafts over the scene. In wait: Tsarnaev is pictured above just down the street from the site of the bomb blast . Approaching: Tsarnaev, circled in white, is seen here walking up to the spot where he dropped the explosive . Less than 30 minutes later, Tsarnaev calmly walked into a Whole Foods store in Cambridge and bought a half-gallon of milk. Jurors were shown surveillance video of him making the purchase and then returning to the passenger side of a car parked in the lot. He then strangely runs back into the store to exchange the gallon of milk for another and then returns to the car. Tsarnaev's defense attorneys cross-examined a witness who said the time stamps on the Whole Foods CCTV was approximate, but prosecutors countered that with a receipt of Tsarnaev's purchase confirming the time for that day was correct. Prosecutors also showed jurors tweets from what they identified as two accounts of Dzhokhar Tsarnaev. 'If you have the knowledge and the inspiration all that's left is to take action,' he tweeted April 7, a little over a week before the bombings. 'I want the highest levels of Jannah,' he tweeted March 10, referring to the Islamic concept of paradise. 'I want to be able to see allah every single day for that is the best of pleasures.' After the blasts: Dzhokhar Tsarnaev is seen entering a Whole Foods in Cambridge, Massachusetts just 30 minutes after the explosions . Errand: Surveillance footage from the Whole Foods shows the younger Tsarneav buying a carton of milk and then checking out . Not the driver: After leaving the store, Dzhokhar is seen walking in the parking lot and entering a waiting car through the passenger-side door . Wrong milk: Dzhokhar was seen re-entering the store to exchange the bottle of milk he purchased for another . Timing: Tsarnaev's lawyers cross-examined a witness who said the time stamps on the surveillance video were approximate, but Whole Foods provided a receipt for Tsarnaev that proves they were correct on that day . An exterior view of the Whole Foods in Cambridge, Massachusetts where Dzhokhar Tsarnaev bought a bottle of milk after the Boston Bombings . In January, three months before the bombings, he tweeted: 'I don't argue with folks who say islam is terrorism it's not worth a thing, let an idiot remain an idiot.' Jurors also heard from victims of the bombing. Jessica Kensky told how she and her husband, Patrick Downes, each lost a left leg in the 2013 attack. After more than 18 months of surgeries and consultations with doctors around the country, she came to the painful conclusion that her right leg would have to be amputated, too, she said. 'I did not want to become a bilateral amputee,' Kensky said. 'I wanted to paint my toenails, I wanted to put my feet in the sand, and I wanted to do all these things. To lose the second leg was a gut-wrenching, devastating decision.' On the run: This FBI video shows Dzhokhar Tsarnaev fleeing the scene of the Boston bombing after setting his explosive. He was pictured carrying the backpack earlier in the day . Fleeing: Tsarnaev is pictured again, highlighted above, fleeing from the carnage he helped create . Facing death: Dzhokhar Tsarnaev, 21, is picturted above with a defense attorney in a court sketch from Monday 9 March. Federal prosecutors hope to secure the death penalty against him for his role in the bombings . Chilling: Dzhokhar Tsarnaev tweeted this message around two hours after he detonated the bomb . Also testifying Monday was a woman whose close friend, 23-year-old Lingzi Lu, died in the second bomb blast. Danling Zhou said Lu grabbed her arm after the first bomb exploded, looking panicked, and said 'What happened?' and 'What should we do?' Before Zhou could answer her, the second bomb exploded. Zhou said she looked in front of her and saw a man whose legs had been blown off. When she looked at Lu, she thought she would be OK because she seemed to still have her arms and legs, Zhou said. Trial: Tsarnaev's case is being heard at The John Joseph Moakley United States Courthouse in Boston . She found out later in the hospital that Lu had died. Both women grew up in China and were graduate students at Boston University. Prosecutors say the Tsarnaevs carried out the bombing to retaliate against the U.S. for wars in Iraq and Afghanistan. During opening statements, a prosecutor cited a hand-scrawled note Dzhokhar Tsarnaev left on the walls of the boat he was captured hiding in and said he believed 'he was a solider in a holy war against Americans' and had 'taken a step toward reaching paradise.' Three people died and more than 260 were injured when two pressure-cooker bombs filled with shrapnel exploded near the finish line.
Footage compiled by FBI shows Dzhokhar Tsarnaev on day of bombing . Seen walking through Boston with brother Tamerlan before twin blasts . Tsarnaev stops outside restaurant, calls brother and waits for explosion . While shocked crowds turn to look, he escapes before second blast . Security footage has him still in the frame when deadly blast occurs . Later seen running through the streets without his backpack, pushing his way through the crowds . Just 30 minutes later, he is seen calmly shopping for a gallon of milk at a Whole Foods store in Cambridge . Tsarnaev, who is facing death penalty, admits carrying out the attack . Defense attorneys say he was influenced by his older brother, who was killed days later in a gun battle .