The former FBI chief had indeed wiretapped the late civil rights leader, but not on his own authority and initially not for President Lyndon Johnson. King biographer David Garrow wrote in a 2002 Atlantic Monthly article:
"On October 10, 1963, U.S. Attorney General Robert F. Kennedy committed what is widely viewed as one of the most ignominious acts in modern American history: he authorized the Federal Bureau of Investigation to begin wiretapping the telephones of the Reverend Martin Luther King Jr. Kennedy believed that one of King's closest advisers was a top-level member of the American Communist Party, and that King had repeatedly misled Administration officials about his ongoing close ties with the man."
Earlier in the program, Matthews had said that at Mrs. King's funeral, "Senator Ted Kennedy reminded us of the role his brothers had played with Dr. King, getting him out of jail back in 1960." This role included Bobby Kennedy inappropriately calling the sentencing judge in the case. There's strong reason to believe the Kennedys' sudden interest was politically motivated. Kennedy's call took place only days before the 1960 presidential election. So grateful was Dr. King's father that he announced, "Because this man was willing to wipe the tears from my daughter (in-law's) eyes, I've got a suitcase of votes, and I'm going to take them to Mr. Kennedy and dump them in his lap."
It's understandable that Teddy Kennedy wouldn't bring up his brothers' role in wiretapping Martin Luther King. But why wouldn't Chris Matthews mention their widely known involvement?