The first time I met Marilynn Rosenthal, we were in New York's Metropolitan Museum of Art. Five weeks had passed since her son Josh, and my father's best friend had died in the terrorist attacks on the World Trade Center, and we were gathered to commemorate his life.

Unlike most mothers in her position, Marilynn was composed. She smiled warmly when she greeted me, and as I found myself smiling back, I na'vely wondered if it was appropriate for people to smile at memorials. It was clear that Marilynn understood the magnitude of the tragedy, but she wouldn't permit self-pity; that just wasn't her. Instead, she celebrated her son and channeled her energy into her search for understanding.

Marilynn continued that search until she died of aggressive cancer last month. She was 77.

Because most University of Michigan students knew her as Professor Rosenthal, her desire for knowledge would seem normal, even unremarkable. She was a medical sociologist who wrote eight books, including "The Incompetent Doctor: Behind Closed Doors" and "Medical Mishaps: Pieces of the Puzzle." After all, most professors engage in research, write books and have PhDs.

But what professor travels halfway around the world to meet the mother of the man who murdered her son?

After Josh's death, Marilynn pursued every available resource to understand what had happened on Sept. 11, 2001. She went to the government, studied the Quran, even visited the restaurant in Florida where the hijackers ate lunch after their flying lessons. She used her share of the Sept. 11 Victims Compensation Fund to start the Ford School of Public Policy's Josh Rosenthal Education Fund Lecture, given each year to help the community objectively understand the cross-cultural challenges facing our society in the wake of the terrorist attacks.

In 2006, she testified at the trial of Zacarias Moussaoui, sometimes dubbed "the 20th hijacker." In her testimony, Marilynn contended that Moussaoui did not deserve the death penalty, because the case against him was weak. She told the jury, "We're not going to get caught up in a whirlpool of frustration and sadness and anger."

And while the Bush Administration called the terrorists savages, Marilynn came to know her son's murderer as "another mother's son." She researched the life of Marwan al-Shehhi, the young man who flew United Airlines Flight 175 into the South Tower of the World Trade Center and killed Josh. She traveled to the United Arab Emirates to try to meet with al-Shehhi's mother, talking to his relatives and visiting his hometown. And she learned that the woman was another son's anguished mother.

For Marilynn, though, her desire for understanding was hardly an unhealthy obsession. When we met to catch up, she would spend most of the discussion asking about my college experience before mentioning her own work. She described with unassuming passion her plans to compile her research into a book about the lives and connected fates of Josh and al-Shehhi. To her, it was a story that needed to be told - a story that she needed to tell.

And while Marilynn's search had nothing to do with bitterness, it had perhaps even less to do with the publicity she attracted. When she introduced Lt. General Brent Scowcroft as the speaker at Josh's first memorial lecture in 2002, the media largely bypassed the former national security advisor and focused instead on Marilynn. After the speech, my dad mentioned complimented Marilynn for telling us, "Don't you know? None of that matters."

It really didn't matter. No matter how many times I saw her on CNN, to me, Marilynn was the advisor who once ticked off my parents by suggesting that I bartend to supplement my 16-year-old dreams of musical theatre stardom. She was the teacher who asked me challenging questions about my first freshman courses when everyone else just wanted to know if I liked my professors. She was the friend who gave me a hug at last fall's memorial lecture, despite the line of important people jockeying for her attention. And she was the mentor who taught me that good can come of evil.

She was the good.

Emmarie Huetteman is an associate editorial page editor. She can be reached at huetteme@umich.edu.