On July 25, Kennedy pleaded guilty to leaving the scene of an accident and was given a sentence of two months in jail, suspended. That night, he gave a national broadcast in which he said, "I regard as indefensible the fact that I did not report the accident to the police immediately", but denied driving under the influence of alcohol and denied any immoral conduct between him and Kopechne. Kennedy asked the Massachusetts electorate whether he should stay in office and, after getting a favorable response, he did so.
In January 1970, an inquest into Kopechne's death took place in Edgartown, Massachusetts. At the request of Kennedy's lawyers, the Massachusetts Supreme Judicial Court ordered the inquest be conducted in secret. The presiding judge, James A. Boyle, concluded that some aspects of Kennedy's story of that night were not true, and that "negligent driving appears to have contributed to the death of Mary Jo Kopechne." A grand jury on Martha's Vineyard staged a two-day investigation in April 1970 but issued no indictment, after which Boyle made his inquest report public. Kennedy deemed its conclusions "not justified." Doubts about the Chappaquiddick incident generated a large number of articles and books over the next several years.
Kennedy easily won re-election to another term in the Senate in 1970 with 62 percent of the vote against underfunded Republican candidate Josiah Spaulding, although he received about 500,000 fewer votes than in 1964.