The body of Annie Le, 24, was found in the wall of a Yale University laboratory building Sunday.
"She was also really tenacious and had a sense of humor that was never far away, and she was tougher than you'd think by just looking at her," Le's roommate, Natalie Powers, told a crowd of hundreds gathered on campus for the slain 24-year-old's vigil Monday.
Le's body was found inside a wall at a Yale medical school building Sunday, the day she was to be married to her college sweetheart, Jonathan Widawsky, a graduate student at New York's Columbia University. She disappeared five days before her wedding. 
Watch timeline leading up to Le's death »
Le and Widawsky attended the University of Rochester together, where Le majored in cell and developmental biology with a minor in medical anthropology.
In a self-profile she wrote for the National Institutes of Health's undergraduate scholarship program, Le called her biology studies "interesting" but said she would like to pursue a research career in medical anthropology, "which has highlighted the severity of health issues in societies worldwide."
She further wrote that she would one day like to work for the NIH or become a professor.
Once at Yale, she majored in pharmacology and worked long hours in the lab where she was found dead this week. Watch how Le's body was found »
Le was scheduled to finish her postgraduate program in 2013 and had recently decided the topic of her dissertation: the effects of certain proteins on metabolic diseases like diabetes, reported the Yale Daily News, the campus newspaper.
"She was probably the most brilliant person I've ever met in my life," her high school friend, Laurel Griffeath, told NBC's "Today" show, "but what made her more amazing was that there was an intersection of intelligence and personality and ability."
Le impressed her peers and teachers long before delving into complicated medical research.
Originally from Placerville, California, Le graduated in 2003 from Union Mine High School, where she was named "best of the best" and "most likely to be the next Einstein," according to CNN affiliate WFSB-TV in New Haven.
Principal Tony DeVille told Le's hometown newspaper, the Mountain Democrat, that she was "one of the bright spots in the school's history."
But she didn't excel solely in academic situations. Friends and professors gush when speaking of Le's vibrant personality and her sense of humor.
Le "was as good a human being as you'd ever hope to meet," Powers said at the vigil. Watch why police say killing not random »
Griffeath said Le knew how to balance her social life and academic responsibilities as well.
"She cared about people and she was funny, and she didn't sacrifice one part of her life for another like a lot of people kind of seem to," Griffeath said on "Today."
Thomas Kaplan, editor-in-chief of the Yale Daily News, described Le as "very outgoing, a warm person."
"She was diminutive in stature, but certainly not in personality, and that's what I think just makes this so sad for everyone, regardless of whether you knew her," Kaplan said of the 4-foot-11 scholar.
Friends describe Widawsky as the perfect match for Le. The portrayed a young couple deeply in love, constantly on the phone with each other and eager to exchange vows.
Le tackled wedding planning with the same zeal she brought to her research, friends said.
"She was just so excited about this wedding and everything from, you know, her flowers to her wedding dress and just certain details about it," Vanessa Flores, a friend and former roommate, told CNN. "We talked about this back in 2008. She was already thinking about the weather -- whether June, July was going to be too hot." Watch Flores describe Le's plans for "her dream day" »
Friend Jennifer Simpson told CBS' "The Early Show" that she was heartbroken for Widawsky.
"Jon is a wonderful person," Simpson said. "He is very mild-mannered, very soft- and well-spoken, but very fun."
Despite Le's zest for life, she was always careful and aware of her surroundings in New Haven, a city with about 124,000 people and its fair share of crime.
"She doesn't walk around at night by herself. If she had to work late, she would make sure someone could come pick her up or walk with her," Simpson told "The Early Show."
Friends say they can think of no one who would want to hurt her. She was friendly with everyone, they say, and if someone had threatened or intimidated Le, her friends and family would have known about it.
New Haven police spokesman Joe Avery has said Le's killing was not random, and authorities and those familiar with the campus say there are only a handful of people with access to the building where her body was found.
The uncertainty surrounding Le's killing -- and the possibility that one of its own is behind the crime -- has left the Yale campus frightened, Kaplan said.
"Only Yalies had access to that basement, and that seems to point to someone in our community being involved in this," the editor said.
Said Powers at the vigil, "That this horrible tragedy happened at all is incomprehensible, but that it happened to her, I think, is infinitely more so. It seems completely senseless."
