Boston Marathon trial retraces the footsteps of bomber brothers

Using surveillance videos and photos, prosecutors in the Boston Marathon trial played an FBI montage Monday that traced the footsteps of the Tsarnaev brothers moving through cheering crowds, then detonating two pressure-cooker bombs in one of the worst terrorist attacks in U.S. history.

The pictures, most never seen before, were culled from tens of thousands of images the FBI collected after the April 2013 blasts, which killed three people and injured more than 260 others. Investigators soon zeroed in on more than 70 images showing Dzhokhar Tsarnaev and his older brother, Tamerlan, each wearing a dark jacket and black backpack, nonchalantly walking through the marathon spectators.

After a while they separated, but soon called each other, speaking briefly on their cellphones.

Then the bomb detonated by Tamerlan exploded. The crowd around Dzhokhar leaned to the left, trying to make out what had happened. Dzhokhar also looked that way. By this time, his backpack was on the ground, and he started walking to the right.

Then the second bomb went off; both devices were detonated by cellphones and remote control devices.

Dzhokhar Tsarnaev, 21, is charged with 30 counts, 17 of which carry the death penalty. Tamerlan was killed in a police shootout several days after the bombing.

Defense lawyers concede that Dzhokhar was there and that he set off the second bomb, but maintain he was merely a pawn of his older, more radical brother.

On the third day of the trial, the government also released for the first time some of Dzhokhar’s tweets before and after the attack. Prosecutors hope the tweets will portray him as an Islamic extremist and rebut defense claims that he was under his brother’s spell.

In March 2013, Dzhokhar Tsarnaev tweeted, “I want to be able to see Allah every day for that is the best of pleasures.” He also wrote, “listen to Anwar al Awlaki … you will gain an unbelievable amount of knowledge,” and, “pray for the oppressed. It is your duty.”

Awlaki, an American citizen, was an Al Qaeda leader and recruiter killed in a 2011 U.S. drone strike.

Two days after the Boston bombings, Dzhokhar sent his last tweet: “I’m a stress free kind of guy.”

The new pictures shown to the jury Monday also appeared to illustrate the debate over what role Dzhokhar played in the attack, a question that could determine whether he is sentenced to death.

In the images, Dzhokhar is almost always a few steps behind his brother. Tamerlan is almost always looking ahead, but Dzhokhar looks to his right several times to watch the runners on Boylston Street.

The montage, assembled by FBI forensic expert Anthony Imel at the bureau’s lab in Quantico, Va., shows the brothers reaching the Boylston Street sidewalk in front of Whiskey’s bar and steakhouse. They round the corner and start threading their way through the crowd.

At one point, Tamerlan seems so determined to reach his location that he bumps into a woman and does not turn to look or excuse himself. He keeps walking.

By the Back Bay Social Club, Dzhokhar seems more interested in the race than in watching where he is going. He stays a few steps behind Tamerlan.

When they reach the front of the Forum restaurant, Tamerlan walks ahead and out of the picture.

Dzhokhar stops and elbows his way into a group of spectators along the race barricade. His backpack is set on the ground, next to his feet. Dzhokhar looks to his left, in Tamerlan’s direction. They are about a block and a half apart. Dzhokhar calls him using a cellphone account he established on April 14, 2013, “one day before the marathon,” Imel testified.

The time is 2:49:06 in the afternoon. The call lasts 19 seconds.

Two minutes later, at 2:51 p.m. there is a second cellphone call, this one from Tamerlan to Dzhokhar.

The first bomb goes off moments later. Everyone in the crowd looks to the left, including Dzhokhar.

“They were alerted to the first explosion,” Imel said. “Everyone was turning left to that explosion.”

Dzhokhar starts to walk the other way. Only at one point does he clearly turn to look behind himself. “He’s looking back at where he was standing,” Imel said.

Just as Dzhokhar leaves the video screen, the second bomb goes off.

The government insists that the phone calls between the brothers strongly suggest they were partners in the attack.

In more images, Dzhokhar continues to walk away. People rush past him; he keeps walking and looks back only occasionally.

He reaches the corner of Fairfield and Boylston streets. There, he starts to trot a bit. But he does not seem alarmed. His head is held high, his jaw slightly cocked as he leaves Boylston Street.

richard.serrano@latimes.com

Twitter: @RickSerranoLAT