On Thursday, in honor of the anniversary, JoAnn and Hank Zywicki went to their daughter's grave.
They'd driven up from their retirement development in Florida, all the way to Pennsylvania, to a little town near where they and Tammy had been born.
Did they really want to do this?
They weren't sure, but there is no surefire happy way to mark the 20th anniversary of a daughter's unsolved murder.
On the way to the grave, they stopped to see Fallingwater, the famous Frank Lloyd Wright home, thinking how much Tammy would have liked it. They have a lot of "Tammy-would-have-liked-this" moments.
This place, this movie, this cat, this lasagna.
What Tammy wouldn't have liked, they know, is for her death to ruin their lives, or the lives of her three brothers, and they've trained themselves not to let it, instead letting the thought of what Tammy would have liked sharpen their own appreciation of things.
Tammy, the art lover and photographer, would have liked the way the light played on Frank Lloyd Wright's house, the trees, the stone, the water.
They thought about that last Thursday.
Then it was on to the cemetery.
Toward the end of August 20 years ago, Tammy Zywicki's parents made a different drive, to the Pennsylvania Turnpike to say goodbye to their only daughter at the turnpike entry.
They hugged Tammy and her younger brother, Daren.
"See you at Christmas," they said.
Tammy drove off in her 1985 Pontiac, en route to her senior year at Grinnell College, a small liberal arts school in Iowa, where she played soccer, studied Spanish and took photos. She dropped her brother off at his Northwestern University dorm, and headed west, alone.
The last time anyone saw her alive, in the middle of the afternoon of Aug. 23, Tammy was standing along I-80 near LaSalle, Ill., next to her car.
Hardly anyone carried cellphones in 1992. Back then, a stranded motorist was truly stranded. A parent could wait a very long time before learning a child was in trouble.
At home in New Jersey on that Sunday night, JoAnn and Hank Zywicki waited for Tammy to call and say she'd landed safely at Grinnell. When too many hours passed, Mrs. Zywicki called the campus police.
The police checked Tammy's dorm, looked for her car on campus. Somebody said, "I thought I saw her."
The next morning the Illinois State Police reported her Pontiac abandoned along I-80.