Dateline investigates the murders of several women found dead along Gilgo Beach in Long Island, New York.

During The Hunt for the Gilgo Beach Killer, Heuermann's former neighbor Jimmy Mack speaks out in his first TV interview, telling Dateline that he "immediately" had a bad feeling about Heuermann. Additionally, Mack revealed that they had a "confrontation" after Heuermann allegedly threatened to cut the tires of a car in Mack's driveway that partially blocked the sidewalk.

The special also examines the death of Shannan Gilbert, whose remains were found on Gilgo Beach in December 2011. Speaking out for the first time since Heuermann's arrest, Shannan's sister calls for Suffolk County Police Department to reopen her sister's case.

In a Dateline NBC exclusive, lead detectives speak out about the investigation into once-prominent South Carolina attorney Alex Murdaugh, convicted last March of murdering his wife Maggie and son Paul.

For the first time, South Carolina Law Enforcement Division investigators Britt Dove and David Owen speak out about the moment they discovered video evidence proving Alex was at the scene of the murders when they occurred. Dove explained to NBC News' Craig Melvin that after listening to the video "three to four times," he was in "disbelief." Owen added he knew at that moment the case had been blown wide open, saying: "I can prove that Alex was lying to me."

The Murdaugh Murders: Inside the Investigation also features an interview with the former Murdaugh family housekeeper Blanca Turrubiate Simpson, who opens up about her unique history with the Murdaughs, as well as Judge Clifton Newman, who presided over the murder trial.