MEXICO CITY (AP) — The parents of a Finnish activist killed when a humanitarian caravan was ambushed in a remote Indian region of Mexico pleaded on Tuesday for justice in the case.

Jyri Antero Jaakkola, 33, was slain April 27 along with a Mexican activist when gunmen attacked human rights observers and leftist activists attempting to reach a Triqui Indian village mired in a violent feud between rival political factions.

Nobody has been arrested nearly four months later.

His parents, Eeva-Leena Jaakkola and Raimo Jaakkola, traveled to Mexico to meet with prosecutors. They pleaded for President Felipe Calderon's help in pushing the case forward.

"Our son died when he was trying to help people fighting for their fundamental rights. He wanted to dissuade violence with his presence as a foreigner, but they killed him," Eeva-Leena said at a news conference in Mexico City.

Police rarely venture into San Juan Copala, an Indian village in the southern state of Oaxaca. The village's violence can be traced back at least 40 years to a struggle for patronage money from state political bosses in the remote Triqui Baja area of the Sierra Mixteca, where an estimated 10,000 ethnic Triquis live.

The upheaval has become more pronounced over the past two years.

In 2007, a leftist group of townspeople known as Multi declared themselves an "autonomous municipality," intent on running San Juan Copala without interference from state or federal authorities. They are opposed by a rival organization known as Ubisort, which Multi claims has the support of the state government.

Organizers of the ill-fated caravan have accused Ubisort of being behind the attack.

Ubisort denies the allegation, and some of its members have accused Multi supporters of staging the attack a ruse to gain public sympathy.

In May, Multi leader Timoteo Alejandro Ramirez and his wife were killed by gunmen. Last month, local Ubisort leader Anastasio Juarez Hernandez was shot to death.

Both sides accuse each other in those deaths, and neither case has been resolved.

The London-based human rights organization Amnesty International joined Jaakkola's parents in demanding justice.

Alberto Herrera, Amnesty's representative in Mexico, said the case was emblematic of the impunity surrounding attacks on human rights activists in Mexico.

"If the authorities are committed to end impunity in attacks against human rights defenders they should show it," Herrera said at the news conference.