TEGUCIGALPA, Honduras — The Honduran police have arrested a high-ranking executive with a hydroelectric company in connection with the 2016 killing of an activist who led a decade-long fight against a dam project, saying that he had helped plan the crime.

The executive, Roberto David Castillo Mejia, was executive president of the Honduran company that is building the dam, Desarrollos Energéticos S.A., or Desa, at the time the activist, Berta Cáceres, was shot and killed.

Mr. Castillo was arrested on Friday at an airport in San Pedro Sula, in northern Honduras, as he was about to fly to Houston, news reports said, citing the prosecutor’s office. The Public Ministry said Mr. Castillo was “the person in charge of providing logistics and other resources to one of the material authors already being prosecuted for the crime,” according to Reuters.

It was at least the ninth arrest in the killing of Ms. Cáceres, 43, a teacher who had battled to block construction of the Agua Zarca Dam along the Gualcarque River, which is sacred to her Lenca people. Ms. Cáceres, who in 2015 was awarded the Goldman Environmental Prize, had faced numerous threats and the killings of other members of her organization.