MEXICO CITY (AP) — The U.N. human rights office in Mexico called for justice Wednesday in the case of an anti-dam activist who was killed in the southern state of Oaxaca on Jan. 23.

Fidel Heras Cruz had opposed plans to build dams on the Rio Verde river, and the U.N. office said he had reportedly received a death threat two days before he died.

Heras Cruz was shot to death near the town of Jamiltepec, Oaxaca, near Puerto Escondido. The office said that seven rights activists were killed in Mexico in 2020, and the lack of punishment makes activists more vulnerable.

“The perception that the defense of human rights or the defense of land can be weakened by killing them (activists), is strengthened every time a killing goes unpunished,” the U.N. human rights representative, Guillermo Fernández-Maldonado, wrote in a statement.

Heras Cruz had also reportedly opposed gravel, rock and sand extraction from the river bed, a lucrative but damaging industry.

In September, Mireya Rodríguez Lemus was found dead with marks of violence in the northern state of Chihuahua. Rodríguez Lemus was a founder of a transgender advocacy group and a promoter of AIDS education and prevention campaigns.