BOSTON - A woman testifying from a wheelchair Monday in the Boston Marathon bombing trial recalled shielding her husband from the sight of his mangled leg, being pushed to the ground by a bystander frantically trying to extinguish the flames on her body, and coming to grips with becoming a double amputee.

Jessica Kensky said 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."

Kensky's account came during the third day of testimony in the federal death penalty trial of bomber Dzhokhar Tsarnaev, whose lawyers have acknowledged his involvement but insist he was influenced by his older brother, Tamerlan, who was killed during a getaway attempt days after the bombings.

Jurors also watched a timeline video compiled by the FBI using surveillance video from stores and restaurants near the marathon finish line. The video, which shows both brothers' movements around the time of the bombings, focuses on Dzhokhar and shows him carrying a backpack until he gets to the front of the Forum restaurant, when he is shown dropping the bag from his shoulder.

As the first bomb explodes, the video shows everyone in the crowd turning toward the blast. Tsarnaev does not look in that direction and instead begins to walk in the other direction.

Seconds later, the second bomb explodes, and Tsarnaev, who prosecutors say detonated the second bomb, is seen running with a crowd.