The deal would give Bukele possession of individuals who threatened to expose the alleged deals his government made with MS-13 to help achieve El Salvador’s historic drop in violence, officials said. For the Salvadoran president, a return of the informants was viewed as critical to preserving his tough-on-crime reputation. It was also a key step in hindering an ongoing U.S. investigation into his government’s relationship with MS-13, a gang famous for displays of excessive violence in the United States and elsewhere.