The long-lasting impact of the Boston Marathon bombing was brought home to jurors as the loved ones of two of the people killed in the attack described their profound loss.

The testimony came on Wednesday, the second day of the penalty phase in the trial of convicted bomber Dzhokhar Tsarnaev.

The jury first heard from the family of Massachusetts Institute of Technology police officer Sean Collier, who was shot and killed by Tsarnaev and his brother as they tried to flee days after the bombings.

Joseph Reynolds, Collier's stepfather, said his wife could not get out of bed for months after her son's death and has still been unable to return to work, two years later.

Reynolds and Collier's brother, Andrew, described Sean Collier as a kid who always had a strong sense of right and wrong, even putting bugs outside rather than killing them.

"He was a cop at an early age," Reynolds said.

Three people were killed and more than 260 wounded when Tsaranev and his brother, Tamerlan, detonated two pressure-cooker bombs near the marathon's finish line on April 15, 2013. Tsarnaev was convicted earlier this month in the bombings and in Collier's killing.

Tsarnaev's lawyers say Tamerlan masterminded the bombing and recruited his impressionable younger brother, then 19. They contend that Dzhokhar does not deserve the death penalty.

But prosecutors have called a long list of victims to argue that he deserves the death penalty for his crimes. The same jury that convicted Tsarnaev will decide his punishment.

Lingzi Lu, a 23-year-old Boston University graduate student from China who was killed in the bombing, was remembered as a highly intelligent, vivacious young woman who took pleasure in even the smallest things, especially food.

"Everything you cook for her, she say, 'It's so good. It's awesome,'" said Jinyan Zhao, a surrogate aunt to Lu. She called Lu "a beautiful nerd."

Jurors also watched a video of a eulogy her father gave at a memorial service at BU. In it, Lu's father calls her "the family's Shirley Temple" and "the little elf and jolly little girl" who brought everyone in the family "ceaseless laughter, lightheartedness and fun."

Tsarnaev's lawyers on Wednesday tried to blunt the impact of a photo of Tsarnaev giving the finger to a security camera in his jail cell three months after the bombing.

His lawyers showed the jury video clips of him looking into the camera, apparently fixing his hair in the reflective glass, and then making a slightly angled, two-finger gesture similar to what teenagers often do playfully in selfies. Then he raised his middle finger at the camera.

In an apparent attempt to press the argument that Tsarnaev was a "kid" who was led astray by his big brother, defense attorney Miriam Conrad asked Assistant U.S. Marshal Gary Oliveira if he knew how old Tsarnaev was at that time.

The witness said he didn't.

"You don't know that he was 19 years old?" Conrad asked.

Testimony is scheduled to resume on Thursday.