We brought you our video report on the defaced Vietnam Veterans War memorial last week. Now, the Park Police confirm this afternoon:

The unidentified substance that was found splashed on the Vietnam Veterans Memorial earlier this month was the result of vandalism, the U.S. Park Police said today.

Sgt. Robert Lachance, a spokesman for the Park Police, said the investigation into the incident is continuing, but the detective on the case had ruled it an act of vandalism. Lachance said he could provide no more details because the probe is still underway.

The oily substance was first reported to police the evening of Sept. 7, National Park Service officials have said. Dark blotches were found along a stone curb at the base of the memorial for most of its length, and at least two of the wall’s panels appeared to have had something splashed on them.

Park Service officials said they did not know what the substance was, and at first said it was unclear if it was the result of vandalism or some kind of accident.

Park Service spokesman Bill Line said today that maintenance and preservation crews were still working to remove the stains and marks, but were proceeding with caution to avoid further damage. He said the crews were trying to avoid pushing any residue into cracks or grout in the stone.

“We’re purposefully going to take our time,” he said.

Line said it could take another week or more to clean, but officials remain confident they can remove all the stains.

Here’s our report in case you missed it:

FYI, the Vietnam Veterans Memorial Fund is offering a $5,000 reward to anyone providing information leading to arrest and conviction in the case.