[Updated at 5:58 p.m. ET Wednesday] President Barack Obama will speak at Wednesday evening's memorial service for the victims of Saturday's shootings that killed six and wounded 14 at a political event in Arizona.

The memorial will be at the University of Arizona in Tucson, four days after the shooting outside a Tucson supermarket at an event held by U.S. Rep. Gabrielle Giffords. The congresswoman was shot in the head and was in critical condition at a hospital Wednesday.

In the days since the shooting, relatives and friends of the slain have spoken about who they were.

Christina Green, 9

A neighbor brought Christina to the event to meet Giffords because the girl had recently been elected to the student council at Mesa Verde Elementary School. The neighbor, Susan Heilman, was shot three times and is recovering, but is struggling emotionally with the girl's death, said her husband, Bill Heilman.

Born on September 11, 2001, Christina entered the world "on a tragic day and she went out on a tragic day," said her father, John Green.

"There's going to be a lot of those kind of moments that - I had one this morning, just waking up. She comes up and says, 'Daddy, it's time to get up.' She didn’t do that this morning," Green told CNN on Sunday.

Christina was the granddaughter of Dallas Green, a former Major League Baseball manager who guided the Philadelphia Phillies to a World Series title in 1980. Her father is a scout with the Los Angeles Dodgers.

Christina embraced the sport and was one of the few girls playing with her local Little League. She loved animals and thought about becoming a veterinarian.

Her mother, Roxanna Green, said Christina "was a great friend, a great sister, a great daughter."

"I was so proud of her. And I just want everyone to know … we got robbed. She got robbed of a beautiful life that she could have had," Roxanna Green said.

Bill Heilman said the Greens have reached out to him and his wife.

"To anyone that's a parent, to me, that's a level of strength that’s almost unimaginable," Heilman said this week. "I guess if I were to say who, if anyone, could handle something like this, it may well be them. But I think the reaction is too much to expect out of anyone, and it just blows me away the grace that they’re showing."

Gabriel "Gabe" Zimmerman, 30

Zimmerman, a Tucson native and director for community outreach on Giffords' staff, was engaged to be married.

He proposed to his girlfriend over the summer, his mother, Emily Nottingham told CNN affiliate KGUN.

"They had a lot of plans about what they might have done, and who knows where life might take you," she told KGUN. "It's a reminder that life can change suddenly."

He was an avid runner and had twice hiked through the Grand Canyon. He previously worked with troubled children at a treatment facility, and he served on the board of several children's groups, including Child and Family Resources Inc. That organization's CEO, Eric Schindler, told KGUN that Zimmerman, who joined Giffords' staff in 2006, became interested in politics after he received a master's degree in social work.

"There were always people who were half-joking, half-seriously chiding him about when he was going to run for office. He seemed to have that innate calling," Schindler told KGUN.

SEE PICTURES OF THE SIX WHO WERE KILLED

U.S. District Judge John Roll, 63

Roll, a Pennsylvania native, was a U.S. District Court judge for the District of Arizona who had served the legal system for nearly 40 years. He began his career as a bailiff in Pima County Superior Court and rose to be chief judge for the District of Arizona, a position he held since 2006.

According to court records relating to the shooting, Roll came to the Tucson event from Phoenix to discuss the volume of federal cases in Arizona with Giffords. He also was said to be at the event to support Giffords, his friend.

Matthew Bowman, who was a law clerk for Roll about six years ago, was loved and respected by everyone who encountered him.

"In his chambers, he dealt with a lot of people on a daily basis, (from) jurors to lawyers to other judges ... and he treated everyone with the highest level of courtesy and respect and dignity that he felt like they deserved, because they were human beings," Bowman, now a lawyer in Washington, D.C., told CNN.

Roll received death threats two years ago after he ruled that a $32 million civil-rights lawsuit filed by illegal immigrants against a rancher in the state could proceed. No link to those threats and Saturday's shooting have been made.

"He lived his life not really worrying about (threats and controversy),"  Bowman said. "If a precaution needed to be taken, he took it, but he really lived his life focused on the people who came into his life, his dedication to God, to his family, to his staff and to really everybody he encountered."

Rolls, a father of three, was "greatly dedicated to his family and the family of his staff," Bowman said.

"We would exchange notes throughout the year if I was involved in an important case or if he was, and it’s really hard to think about him not being there anymore," he said.

Dorwan Stoddard, 76

Witnesses said Stoddard, a retired construction worker, was trying to shield his wife, Mavy, when he was shot in the head and fell onto her. Mavy was shot three times in her legs but is expected to recover.

Stoddard's daughter Penny Wilson, who wasn't at the event, told reporters Tuesday that her mother has confirmed the account.

"He heard the shots and covered my mom with his own body and protected her and saved her. Mom definitely felt that way," Wilson said.

Another daughter, Angela Robinson, said that Mavy didn't know she was shot until she arrived at the hospital with her husband.

The couple attended the Church of Christ in Tucson. Dorwan built a room for attendees with small children.

"They both fed the needy, housed the needy, gave money to the needy and gave clothes to the needy. They were very important to us," the Rev. Michael Nowak told CNN.

Dorwan and Mavy knew each other as children. After both lost their spouses, they reunited and married. They were together for nearly 15 years.

"They were inseparable. You saw one, you knew the other one wasn't far behind," Nowak told KGUN.

Dorothy Morris, 76

Morris - friends called her "Dot" - was in line with her husband to meet Giffords when the shooting started, KGUN reported. Her husband, George, was wounded. The couple had been married for 55 years and lived in Arizona's Oro Valley, according to KGUN.

The pair were high school sweethearts in Reno, Nevada, one of their high school friends told KTVN in Reno.

They married in Reno and attended the University of Nevada, said the friend, Merilyn Melton.

Melton said George Morris would often describe Dorothy as his girlfriend or his bride.

"He and Dorothy were one of these devoted couples that were always together," Melton told KTVN.

Phyllis Schneck, 79

Schneck, of New Jersey, was a grandmother who spent winters in Arizona after retiring. She was known for her volunteer work wherever she lived, friends said.

"She always makes friends. She has friends everywhere she's lived," her son, Ernest Schneck, told WABC.

Her son told WABC that she was a registered Republican, though not politically active. But she liked Giffords, a Democrat.

"She just wanted to go down and shake her hand," Ernest Schneck told WABC.

Her husband died in 2007, according to the Daily Record of New Jersey.

- CNN's Casey Wians, T.J. Holmes, Ted Rowlands, Drew Griffin and Jason Hanna contributed to this report.