The investigation into the 1964 murders of three civil rights volunteers by a group of Klansmen, an inquiry that became known as the “Mississippi Burning” case, has come to a close, the Mississippi attorney general announced Monday.

The murders of Michael Schwerner, James Chaney and Andrew Goodman, committed on a remote Mississippi road 52 years ago on Tuesday, prompted an intense federal investigation. That investigation, plus a re-examination in more recent years, led to eight trial convictions and one guilty plea over five decades. One of the masterminds of the murders, a Klansman named Edgar Ray Killen, was convicted by state prosecutors in 2005.

“I am convinced that during the last 52 years, investigators have done everything possible under the law to find those responsible and hold them accountable,” said Jim Hood, the state attorney general, at a news conference. “However, we have determined that there is no likelihood of any additional convictions. Absent any new information presented to the F.B.I. or my office, this case will be closed.”