The Latest on commemorations marking the 15th anniversary of the Sept. 11 attacks (all times local):

8:20 a.m.

Family members of those lost on Sept. 11 are arriving at ground zero for the ceremony marking the 15th anniversary of the attacks.

Some are going into National September 11 Museum, which is open only to victims' families until Sunday afternoon, when the public will be allowed to enter.

About an hour before the official commemoration start, police officers in uniform and bagpipers rehearsed part of the ceremony involving a display of the US flag.

As it has every year, the remembrance will mainly focus on the reading of the names of those killed in the attacks. It will also include moments of silence and the tolling of bells.

Other ceremonies are being held at the Pentagon and at the Flight 93 National Memorial in Shanksville, Pennsylvania.

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12:20 a.m.

Relatives and loved ones of 9/11 victims will convene Sunday to mark the 15th anniversary of the terror attacks.

Organizers have planned some additional music and readings to mark the milestone anniversary at ground zero.

But they are keeping traditions that have made the ceremony a constant in how America remembers Sept. 11, even as ground zero and the nation changes.

The customs include moments of silence and tolling bells, an apolitical atmosphere and the reading of the nearly 3,000 names of those killed in New York, at the Pentagon and near Shanksville, Pennsylvania.

President Barack Obama will speak at an observance at the Pentagon. Hundreds of people also are expected at a ceremony at the Flight 93 National Memorial in Shanksville.