On May 21, 1970, a communiqué from the Weather Underground was issued promising to attack a "symbol or institution of American injustice" within two weeks. The communiqué included taunts towards the FBI, daring them to try to find the group, whose members were spread throughout the United States. Many leftist organizations showed curiosity in the communiqué, and waited to see if the act would in fact occur. However, two weeks would pass without any occurrence. Then on June 9, 1970, their first publicly acknowledged bombing occurred at a New York City police station, saying it was "in outraged response to the assassination of the Soledad Brother George Jackson," who had recently been killed by prison guards in an escape attempt. The FBI placed the Weather Underground organization on the ten most-wanted list by the end of 1970.