(CNN) -- The bodies of three family members of a slain Mexican activist were found dumped near a gas station just outside of Ciudad Juarez, Chihuahua state prosecutors announced Friday.
The victims were identified as Elijah and Malena Reyes Salazar and Louise Ornelas Soto, all relatives of Josefina Reyes Salazar, an outspoken human rights activist who had investigated abuses by the Mexican military and the federal police in the Valley of Juarez. She was killed in January 2010, and two other relatives -- including her brother -- have also been slain.
A message explaining the motive for the latest killings was left on the bodies of the victims by "organized criminals," according to state prosecutor's office spokesman Carlos Gonzalez.
They had been missing for 18 days before their bodies were found in the municipality of Guadalupe Distrito Bravos, Mexico, prosecutors said.
Earlier this week, Amnesty International had urged Mexican authorities to provide protection for the Reyes family.
Friday, the group released a statement condemning the deaths.
"The Reyes family are clearly being targeted in the most brutal way. The Mexican authorities' top priority must be to ensure the safety of other relatives," Susan Lee, director of the Americas program at Amnesty International, said in a statement. "They must also launch a prompt and thorough investigation and bring to justice those responsible for the killings, which were apparently sparked by Josefina Reyes daring to speak out against the explosion of violence in Mexico."
On February 15, the Reyes family home in Guadalupe was burned down by suspects who used homemade petrol bombs.
Journalist Arturo Chacon contributed to this report