Construction at the Obama Presidential Center in Chicago has been suspended after discovery of a noose, a racist symbol in the United States, companies overseeing the project said. The looped rope -- which harkens back to the lynchings of black men in the American South in the 19th and 20th centuries -- was found Thursday morning. "We are horrified that this would occur on our site and are offering a $100,000 reward to help find the individual or individuals responsible for this shameful act," said the Lakeside Alliance, a group of Black-owned construction companies that are building ex-president Barack Obama's center.