In January 2011, someone called the son of John Casias and demanded that he cooperate "or else."

When he asked what the threat signified, the caller said he would be sending "a finger" so that all knew they meant business. The son turned out to be safe, but the message from thugs in Mexico was delivered nonetheless.

"They use these tactics to open doors for kidnapping," Casias wrote in his newsletter , laying out what in retrospect may have been a death foretold. "We have to travel in the mornings," he said of the precarious security situation, "because the bandits usually work at night."

Casias and his wife, Wanda, were found dead in their home a week ago Tuesday, apparent victims of the violence that is plaguing Mexico. Both had been strangled.

The missionaries had spent the last three decades near Monterrey, tending to a community they had built with the help of Liberty Baptist Church in Lewisville.

The newsletters, which he filed under "mission reports," offer a chilling chronology of the violence in this part of Mexico. I found them today while reporting for an editorial that will run tomorrow.

Authorities have not released a motive. But you don't have to go deep into the newsletters to see that the threat of violence was a daily event for the missionaries.

In his last one, dated September-October 2011, Casias said outright that some religious groups are paying the drug cartels for protection from kidnappings:

"These last few days have been very challenging times. To start with every cult is trying to take advantage of the crisis by getting favor with the cartel, thinking that those ruthless murderers will have mercy on them and not kidnap them. All they do is buy time by paying the cartel monthly payments. But they always come back on them."

He also saw no value in these kinds of payoffs:

"These liberal cults think that they will be safer. The cartel will use anyone they can and when they finish using you they kill you. There is no compromise with the devil."

From the newsletter dated May-June 2011: "Praise the Lord that last week we went two days without someone being killed or kidnapped, although several were killed and beheaded near us."

It is also clear that the violence greatly affected the work at the church, which relies on donations and especially on volunteers to do the hands on work. "Before the violence we had support groups coming to help us with construction or whatever," Casias wrote. "But since all the killing and kidnappings, we have had NONE."

In the newsletter of August/September 2010, Casias noted that the mayor of the town had been kidnapped and murdered, his body left on the side of the road "like an animal, hands tied and blindfolded."

"The cartel has NO mercy or value for life. They are ruthless murderers," he wrote.