This picture was taken just a few hours before vandalism was discovered on the Bean. This guy is cleaning the Cloud Gate sculpture, commonly known as "The Bean", located at approximately 98 E. Washington Street in Chicago. There is a woman in the background with a bucket. This is the northwest corner of the sculpture. There was also a flatbed golf cart nearby that it seemed they were using in their work. News reports say that the sculpture was defaced on the northeast corner during the day before 1:30PM on Monday, February 2, 2009. I took this picture at about 10 AM– there were very few people there. Here's a wider picture of the cleaners and a couple more shots from yesterday.
Seems to me that a natural thing to do in the course of the investigation would be to ask these people if they saw anything funny (or maybe they're the ones who discovered the issue and reported it) and also check for images on the day of the incident on Flickr and other sources.
UPDATE, 2/4/9 — I went to the Millenium Park offices and showed them this pic. They work for the park. (Thanks for cleaning the Bean, guys!). Also, the image above is of the *exact* same spot of the defacement.