Accounting for 2/26 in a Museum Devoted to 9/11 Twenty years ago Tuesday, a deadly calling card was left at the World Trade Center. When a truck bomb exploded in an underground parking garage, killing six people, injuring hundreds more and upending daily life in New York, it seemed as if the worst conceivable act of terrorism had been committed. But it turned out to be no more than an awful prelude. "Unfortunately, our calculations were not very accurate this time," one of the 1993 conspirators, Nidal A. Ayyad, was said to have written (in slightly broken sentences) not long after the bombing. However, we promise you that next time it will be very precise and WTC will continue to one our targets in the U.S. Though there is no direct link between the 1993 and 2001 plots, they have long been regarded as points on a continuum. And that is how they will be treated at the National September 11 Memorial Museum, said Alice M. Greenwald, the museum director. She pointed to the least imposing of several artifacts arrayed on a conference table: a clunky, silver Toshiba T1950CT laptop among crumpled "Stop" signs, a bond trader's smudged button-down shirt and a dead firefighter's well-worn turnout coat. "This one object allows us to connect 1993 to 2001," Ms. Greenwald said of the laptop. That is because it was confiscated in 1995 from an apartment in Manila being used by Ramzi Ahmed Yousef, a mastermind of the 1993 attack. The authorities" attention was drawn to the building when a fire broke out there. Officials said that a file on the laptop, labeled "Bojinka," contained detailed plans for a plot in which a dozen airliners were to be simultaneously blown up over the Pacific Ocean. Mr. Yousef was said to have developed this plan with his uncle, Khalid Shaikh Mohammed, the self-described mastermind of 9/11. The laptop will be on exhibit in the museum, as will an axle fragment stamped with the vehicle identification number that led investigators to link a 1990 Ford Econoline van rented from Ryder to the truck used to bomb the trade center. Both objects have been lent to the museum by the Federal Bureau of Investigation. "The F.B.I. and the Department of Justice have been incredible partners," Ms. Greenwald said. They make it possible for us to tell the story. Describing the museum as visitors will find it in 2014, when it is to open, Ms. Greenwald said the gallery devoted to the first attack would be within the physical outline of the north tower foundations. It will be one element in an exhibition devoted to the events leading up to the 2001 attack, what happened on 9/11 itself and what occurred in the aftermath. The most significant symbolic link between the two attacks is a small chunk of rose-colored granite - inscribed "John D" and "mem." It is the only surviving piece of a fountain dedicated to the victims of the first attack, which stood on the World Trade Center plaza. This was where relatives gathered on the Feb. 26 anniversary until it, too, was destroyed. "John D" once read "John DiGiovanni." He was a victim, as were William Macko, Wilfredo Mercado, Robert Kirkpatrick, Stephen Knapp and Monica Rodriguez Smith and her unborn child. The "mem" is from "memoria" - "Esta fuente está dedicada en memoria de aquellos que perdieron sus vidas." "This fountain is dedicated to the memory of those who lost their lives." By custom, the fragment has been placed at the head of the center aisle during the Masses celebrated each anniversary since 2002 in St. Peter's Roman Catholic Church, at 22 Barclay Street. Though the fragment is being lent to the museum by the Port Authority of New York and New Jersey, it will always be made available for this Mass, a museum spokesman said. In fact, he said on Monday afternoon, it was already on its way from the museum office. The Mass is to be celebrated at 10:30 a.m. on Tuesday. Beginning at noon, the names of the dead will be read in a ceremony at the National September 11 Memorial. A moment of silence is to be observed at 12:18 p.m., when the bomb was detonated. The name of Wally P. Travers, of Upper Saddle River, N.J., is not among these victims. He was a bond broker at Cantor Fitzgerald who survived the attack after a five-hour odyssey from the summit of the north tower, Ms. Greenwald said. He made a point of never cleaning the shirt he wore that day. Instead, he kept it as a memento - darkened by smoke and soot - in the back of his closet. That is where his wife found it after he was killed on 9/11.