'You're on fire' - witness recalls Boston blast aftermath

A still image captured from surveillance video shows the moment when a second bomb exploded near the finish line of the Boston Marathon, on April 15, 2013 in this handout video provided by the US Attorney's Office in Boston, Massachusetts, on March 9, 2015. [Photo/Agencies]

The jury on Monday viewed video taken by security cameras near the finish line on Boylston Street showing Tsarnaev walking with a backpack that prosecutors contend held a bomb, leaving it in a crowd in front of a restaurant, making a brief phone call and walking away shortly before the blast.

Defense lawyers contend that Tamerlan Tsarnaev, 26, who died following a gunbattle with police three days after the bombing, was the driving force behind the attack, with Dzhokhar following along out of a sense of submission. By pinning the bulk of the blame on the older brother, defense lawyers hope to persuade the jury in US District Court in Boston not to sentence their client to death.

Prosecutors maintain that the defendant also read jihadist magazines online and "believed that he was a soldier in a holy war against Americans."

On Monday, they showed messages from a pair of Twitter accounts that Tsarnaev maintained, according to FBI agent Stephen Kimball.

Hours after the bombing and using the handle "J_Tsar," Tsarnaev sent the message, "ain't no love in the heart of the city, stay safe people," Kimball said. Tsarnaev also responded to a message sent by another user about a man who had lost his fiancee with the words "fake story," Kimball testified.

Tsarnaev, an ethnic Chechen, also briefly maintained a second Twitter account focused on Islam using the handle "@AL_FirdausiA" and the screen name "Ghuraba," Kimball said.

"Ghuraba means strangers. Out here in the west we should stand out among the nonbelievers as one body," Tsarnaev tweeted, according to Kimball.

Despite his lawyers' admission of responsibility, Tsarnaev has not changed his plea from not guilty.

The bombing killed Martin Richard, 8; restaurant manager Krystle Campbell, 29, and graduate student Lingzi Lu, 23. Massachusetts Institute of Technology police officer Sean Collier, 27, was shot to death three days later.