Live updates: Trial of accused Boston Marathon bomber Dzhokhar Tsarnaev

The trial of accused Boston Marathon bomber Dzhokhar Tsarnaev continues Thursday. Testimony focused on the murder of MIT police officer Sean Collier, who was shot and killed at close range as the Tsarnaev brothers allegedly tried to steal his gun hours after their pictures were broadcast as suspects in the marathon bombings. Collier was shot six times, including three times in the head.

Some jurors gasped and teared up as they viewed gruesome autopsy photos of the gunshot wounds to Collier's head. The head wounds caused "direct destruction of the brain," Renee Robinson, the Boston medical examiner who performed the autopsy, testified. "His heart stopped... He inhaled his own blood."

That was followed by dramatic new video footage from a Shell gas station in Cambridge, where the Tsarnaev brothers allegedly drove after carjacking a Boston man following Collier's murder. The surveillance video shows Dzhokhar Tsarnaev casually shopping for snacks, including a bag of Doritos and cans of Red Bull. Outside, the camera captured carjacking victim Dun Meng jumping out of his Mercedes SUV and running away. As Meng ran, Tamerlan Tsarnaev dashed to the door of the store to alert his brother, who dumped the snacks before both ran back to the SUV and sped away.

"Every time i recall this, I think it is the most terrifying moment, the most difficult decision in my life," Meng said as he took the stand, giving jurors a harrowing account of his dealings with the Tsarnaev brothers that night.

Meng, who is a partner in a company that designs iPhone apps, said he had just been out for a drive when he was carjacked by Tamerlan Tsarnaev, who held a gun to his head and ordered him to drive. He demanded cash and was disappointed to find that Meng only had $45. Along the way, Tamerlan asked Meng if he'd heard about the Boston Marathon bombings. "I did that," Tamerlan said, acccording to Meng. "And I just killed a policeman."

Dzhokhar Tsarnaev later joined his brother in the vehicle, and with Tamerlan at the wheel, the three circled around the Boston suburbs, as the brothers contemplated their next move. Meng testified he could not understand the brothers, who were speaking in a foriegn language. But at one point, Tamerlan asked Meng if his car could be driven out of state. "Like to New York?" Tamerlan Tsarnaev asked.

Testimony continued Thursday afternoon, as prosecutors recounted the brothers' movements leading up to Dzhokhar Tsarnaev's subsequent capture. Yahoo News' Holly Bailey is in the courtroom in Boston covering the proceedings. Follow her reports and the latest developments below.