Remember, Dr. King was in Memphis to help with the sanitation workers' strike.
Also, at that point in the early spring 1968, Dr. King & his team were well on their way with organizing their Poor Peoples Campaign (NOT, for fucks sake, lowering the tax burden on rich folks in some misguided, and non-effective, "trickle down" theory).
Read more about the Poor Peoples Campaign here:
http://en.wikipedia.org/wiki/Poor_People%27s_Campaign
(Exerpt below)
Planning and strategy
Planning for the Poor Peoples Campaign began during a five day retreat on November 27, 1967 in Frogmore, South Carolina.[5] King told his aides that the SCLC would have to raise nonviolence to a new level to pressure Congress into passing an Economic Bill of Rights for the nations poor. When reporters asked King about the campaigns tactics, he sidestepped specific details and focused on the moral dimensions of the crisis.[5] The Poor Peoples Campaign held firm to the movements commitment to non-violence. We are custodians of the philosophy of non-violence, said Martin Luther King, Jr. at a press conference. And it has worked.[2] King originally wanted the Poor People's Campaign to start in Quitman County, Mississippi because of the intense and visible economic disparity there. On March 18, 1968, King visited the town of Marks, Mississippi. He watched a teacher feeding schoolchildren their lunch, consisting only of a slice of apple and some crackers, and was moved to tears. After King's death, the Southern part of the Campaign began in Quitman County, riding a train of mules to Washington, D.C..[6]