From the Wikipedia article about Billy Sol Estes (where it IS mentioned that JFK was considering dropping LBJ from the 1964 ticket - a powerful inducement to "do" something I would think....):

[link to en.wikipedia.org]

Kennedy assassination allegations[edit]

Estes also alleged in the 1980s that he had inside knowledge that Johnson was involved in the assassination of Kennedy.[10][11] In 1984, he provided a voluntary statement to a Grand Jury in Texas alleging that the homicide of a key investigator in the Department of Agriculture case was perpetrated by an aide to Johnson, Malcolm Wallace, upon orders from the then-Vice President.[4] When the Department of Justice asked for more information, Estes responded that he would provide information on eight other murders ordered by Johnson, including the assassination of Kennedy, in exchange for immunity from prosecution and a pardon.[4] According to Estes, Johnson set up the assassination in order to become president.[4] They refused.

Estes reiterated the claim in a book he co-wrote with a French writer in 2003.[11][12] He said that he was not interested in writing the book – published only in France – but that he was offered "a few hundred thousand dollars" to contribute to it.[11] According to the Associated Press, the allegation was "rejected by prominent historians, Johnson aides and family members."[12