NEW YORK — The two terrorist attacks on the World Trade Center, eight years apart, converged Tuesday in the form of a piece of granite, part of a memorial to those who died in 1993 that was itself destroyed on Sept. 11, 2001.
The jagged fragment was displayed during a ceremony marking the 20th anniversary of the 1993 attack.
A bell tolled for a moment of silence at 12:18 p.m., the exact time of the explosion under one of the twin towers that killed six people. More than 1,000 people were injured when terrorists detonated a truck bomb in an underground garage.
Family, friends, and city officials stood near the memorial to those who perished in the 2001 attack, which toppled the same tower targeted in the 1993 explosion.
‘‘There are some days when you can’t remember what he sounded like, but then there are other days when you expect to see him in the morning, when you wake up,’’ Stephen Knapp said after the ceremony, his voice breaking as he remembered his father, also named Stephen. He was 18 when his father died.
On Tuesday, Knapp joined about 50 people — including Mayor Michael Bloomberg and former mayor David Dinkins — for the anniversary ceremony.
Knapp and Michael Macko, who also lost his father, read the victims’ names before New York Police Department bagpipers played ‘‘Amazing Grace.’’
White roses were laid over the six names chiseled into granite over one of the 9/11 memorial’s two reflecting pools, alongside the names of more than 2,700 people killed in 2001 when planes that had been hijacked by terrorists brought down the twin towers.
A wooden box was opened to reveal the piece of broken granite that was once part of the memorial fountain honoring the dead from 1993 on a plaza above the explosion site.