TEGUCIGALPA – Honduran authorities said they were continuing their efforts to determine the masterminds behind the March murder of prominent environmental activist and indigenous leader Berta Caceres.

The Technical Criminal Investigation Agency, or ATIC, “is committed to identifying the masterminds, if there are any, which the investigation will tell us,” Director Ricardo Castro told reporters Thursday after confirming the arrest of a sixth suspect in the killing.

Elvin Rapalo Orellana was arrested Thursday morning by ATIC agents in Zacapa, a municipality in the western province of Santa Barbara.

The 21-year-old Rapalo Orellana is one of the suspected perpetrators and is accused of shooting Gustavo Castro, an environmental activist from the southern Mexican state of Chiapas who was at Caceres’ home when she was gunned down.

The ATIC director said Honduran prosecutors would decide whether it was necessary for the Mexican activist to return to the country to identify Rapalo Orellana as the attacker who shot him and left him for dead, but he added that forensic evidence already points to Rapalo Orellana as one of the gunmen.

Caceres, co-founder and coordinator of the Civic Council of Popular and Indigenous Organizations of Honduras, or Copinh, was shot and killed in the wee hours of March 3 when gunmen who broke into her home in the western town of La Esperanza.

ATIC’s Castro said the investigation into Caceres’ murder “was never declared closed,” adding that it will continue until the masterminds are found.

The other detainees in the case include Douglas Bustillo, army Maj. Mariano Diaz, retired army Capt. Edilson Duarte and Sergio Rodriguez, an employee of Desarrollos Energeticos S.A., or DESA, the private energy company behind a hydroelectric project in western Honduras – known as Agua Zarca – that Caceres opposed.

Authorities also have arrested Edilson’s twin brother, Emerson Duarte, seizing a .38-caliber revolver from that suspect that he allegedly used to kill Caceres.

Bustillo, Diaz and Rodriguez are considered “mid-level masterminds” of Caceres’ murder, while the Duarte brothers and Rapalo Orellana are the suspected gunmen, the ATIC director said.

Caceres, an award-winning environmental activist and Lenca indigenous leader, was the beneficiary of precautionary measures granted by the Inter-American Commission on Human Rights in 2009.

Those measures were assigned after she said she had received death threats from DESA for leading demonstrations by Lenca indigenous communities against the building of the Agua Zarca dam on the Gualcarque River.