ACTEAL, Mexico (AP) _ Hundreds of people prayed and wept Monday at a Mass for 45 people gunned down by a vigilante force six months ago, and many complained the people involved in the slaying remain at large.

``The paramilitaries ... remain free and are preparing to attack us again if we return to our original communities,'' said Ernesto Mendez Paciencia, a survivor of the Dec. 22 attack.

More than 800 people driven from their communities by violence in the surrounding area are to return home on Thursday in a program sponsored by state officials. They are to be accompanied by human rights observers.

The massacre occurred when a pro-government vigilante group, apparently seeking revenge for attacks on government supporters, gunned down members of a group called Las Abejas as they left a church in this hamlet north of San Cristobal de las Casas.

Las Abejas sympathizes with the leftist Zapatista National Liberation Army, but preaches non-violence. Many of those who died were among some 9,000 people in the Chenalho region who have been driven from their homes by threats or attacks.

The government arrested or opened criminal investigations against 150 people in the slaying, and Gov. Julio Cesar Ruiz Ferro was forced to resign after evidence emerged that lower-ranking state officials had collaborated with the vigilante group and ignored early reports of the massacre.

Women in hand-woven Indian shawls lit candles and sang before an altar made of wooden poles and laminated roofing.

Priest Pedro Arriaga assured the worshippers that ``the force of Jesus accompanies us to achieve peace with justice and dignity.''

Survivors complained that some of those involved in the vigilante group remained at large and that other vigilantes operate in the region.