Construction on former US President Barack Obama's future Presidential Center in Chicago has been halted following the discovery of a rope with a hangman's knot.
"We are appalled that this could have happened on our construction site and are issuing a $100,000 reward to help find whoever is responsible for this shameful act," said the Lakeside Alliance consortium responsible for the construction.
The police were also involved.
A rope with a hangman's knot is considered a racist symbol in the USA and is reminiscent of the time of the lynching of African Americans.
The Lakeside Alliance emphasized that there was "zero tolerance for prejudice and hatred" on the construction site.
The rope was therefore already discovered on Thursday morning.
Illinois Gov. JB Pritzker tweeted that there was "no place for hate in Illinois."
The rope with a hangman's knot is not only a "symbol of racism", but also a reminder of "violence and terror" from which black people in the USA have suffered for centuries.
The cornerstone for the Obama Presidential Center was laid in September 2021.
A museum about Obama's political career, a library, classrooms and meeting rooms and places for leisure activities such as basketball are being built in Jackson Park in south Chicago on the shore of Lake Michigan.
Obama, the first black president in US history (2009 to 2017), began his political career in Chicago.
In the USA it is a tradition that previous presidents get a library named after them.
Obama has emphasized that his Presidential Center will become an action-oriented facility designed to "empower the next generation of leaders."