WASHINGTON, D.C. (AP): President Donald Trump  is presiding over his first 9/11 commemoration in office.

Nearly 3,000 people were killed in 2001 when hijackers flew commercial airplanes into New York’s World Trade Center, the Pentagon and a field near Shanksville, Pennsylvania. The president and first lady Melania Trump observed a moment of silence at the White House at 8:46 AM Monday.

The remembrance was scheduled for about the time the first plane struck one of the Twin Towers on the morning of Sept. 11, 2001.

Trump and his wife also are planned to pay their respects at a Pentagon observance. Vice

President Mike Pence is scheduled to represent the administration at an observance at the 9/11 memorial in Shanksville.

Elsewhere, police officers are on hand after a threat referencing Sept. 11 was found written in a bathroom stall in a Pennsylvania school. Officers are patrolling Central Bucks West High School in Doylestown as a precaution Monday.

It’s not clear what the threat said. But principal Timothy Donovan told parents the situation was promptly addressed to ensure the safety of students and teachers. The school will excuse the absences of any students if parents decide to keep their children home.