Cleanup continues at the Lincoln Memorial on Tuesday after it was marred with graffiti. The writing is covered by the white sheet on the wall. (Perry Stein/The Washington Post)

The Washington Monument and the World War II, Lincoln and D.C. War memorials were damaged by graffiti over the holiday weekend.

U.S. Park Police and National Park Service officials said the four sites had graffiti markings that were similar in nature and not considered to be political or racial.

The vandalism was scrawled in black permanent marker. Two of the messages were at the Lincoln Memorial: one in the memorial and another at the foot of the steps. One was found at the World War II Memorial, one at the Washington Monument and one at the D.C. War Memorial.

Other acts of vandalism were found on street signs and utility boxes on the Mall.

Some of the words in the messages were hard to decipher. One message said, “Jackie shot JFK.” Another mentioned the Sept. 11, 2001, terrorist attacks on the World Trade Center. And another part of the graffiti said that “blood test is a lie” and mentioned leukemia, cancer and HIV, saying “get second opinion.”

Cleanup at the Lincoln Memorial after it was marred with graffiti. (Perry Stein/The Washington Post)

Sgt. Anna Rose, a spokeswoman for the U.S. Park Police, said each of the monuments had similar messages. The size of the message varied from about the size of the palm of a hand to as big as a football, officials said.

The incidents probably happened between 9 p.m. and 11 p.m. Saturday, according to officials.

Authorities said they have been told that there was a large crowd around some monuments late Saturday, and they asked anyone who saw anything to come forward with information.

“We understand that there was quite a crowd here Saturday night who may have seen something,” Rose said at a news conference Tuesday in front of the Lincoln Memorial.

Investigators are also working to pull surveillance video from the area and believe that all of the incidents are related. Park Police officials said none of the messages rose to the level of being a hate crime, according to Rose. Those responsible could face vandalism charges, she said.

In 2015, a case was dismissed against a Chinese woman who was suspected of tossing green paint on several D.C. landmarks, including the Lincoln Memorial, after a judge determined she was incompetent to stand trial. ­Jiamei Tian had been charged in 2013 with one count of defacing property after paint was found spattered in Washington National Cathedral.

Graffiti at the foot of the steps at the Lincoln Memorial. (Perry Stein/The Washington Post)

It often takes several treatments to remove graffiti from monuments, and authorities have to avoid causing long-term damage, said Mike Litterst, a spokesman for the National Park Service.

Work crews expect the cleaning to take about two weeks with several rounds of treatments using solvents.

Litterst said that getting the green paint off the monuments in the earlier incident took about a dozen treatments but that “hopefully this won’t be quite as bad.”