Graffiti found at 3 popular monuments in Washington, DC

A U.S. Park Service employee works to clean graffiti off of the Washington Monument, Tuesday, Feb. 21, 2017, in Washington. U.S. Park Police spokeswoman Sgt. Anna Rose said that the messages written in permanent marker were discovered over the holiday weekend at the Lincoln Memorial, the Washington Monument and the World War II Memorial. (AP Photo/Alex Brandon)

WASHINGTON (AP) — The National Park Service says graffiti has been found at the Lincoln Memorial, the Washington Monument and the World War II Memorial.

U.S. Park Police spokeswoman Sgt. Anna Rose said Tuesday that messages written in permanent marker were discovered over the holiday weekend. Similar graffiti was found on a power box along the National Mall.

Graffiti is seen on the Lincoln Memorial, Tuesday, Feb. 21, 2017, in Washington. U.S. Park Police spokeswoman Sgt. Anna Rose said that the messages written in permanent marker were discovered over the holiday weekend at the Lincoln Memorial, the Washington Monument and the World War II Memorial. (AP Photo/Alex Brandon)
Graffiti is seen on the Lincoln Memorial, Tuesday, Feb. 21, 2017, in Washington. U.S. Park Police spokeswoman Sgt. Anna Rose said that the messages written in permanent marker were discovered over the holiday weekend at the Lincoln Memorial, the Washington Monument and the World War II Memorial. (AP Photo/Alex Brandon)

Rose says the message written on the Washington Monument references President John F. Kennedy’s assassination and the Sept. 11, 2001 attacks.

Park service spokesman Mike Litterst says because of similarities in what’s written and the handwriting, it’s thought the graffiti was left by one person.

The Washington Post reports that workers estimate cleaning will take about two weeks. The newspaper reports that officials believe it happened Saturday night and are pulling surveillance video.