An undated file photo of Martin Luther King Jr.

Martin Luther King Jr. attends a news conference in Birmingham, Alabama, May 9, 1963.

Martin Luther King Jr., head of the Southern Christian Leadership Conference, speaks to thousands during his "I Have a Dream" speech in front of the Lincoln Memorial, in Washington, August 28, 1963.

Martin Luther King Jr. addresses marchers during his "I Have a Dream" speech at the Lincoln Memorial in Washington, August 28, 1963.

Martin Luther King, Jr. is welcomed by Baptist youths on arrival in Oslo, Norway, to accept the Nobel Peace Prize, December 8, 1964.

Martin Luther King Jr., second from right, speaks at a news conference next to John Lewis, chairman of the Student Nonviolent Coordinating Committee, in Baltimore, Maryland, April 2, 1965.

Martin Luther King, Jr. chats with his wife, Coretta, left, and civil rights champion Constance Baker Motley before the start of an S.C.L.C. banquet, Birmingham, Alabama, August 9, 1965.

This April 1968 photo released by the MLK Jr. National Historic Site shows the body of Martin Luther King Jr. being carried to Morehouse College in Atlanta, Georgia. (AP Photo/MLK Jr. National Historic Site,Courtesy of Bob Adelman)

The grave of Martin Luther King, Jr., is shown at South View Cemetery, Atlanta, Georgia, April 9, 1968.

The Martin Luther King Jr. Memorial in Washington, August 22, 2011.