Concerns about border security heightened this week as federal officials in Mexico searched for nearly eight tons of sodium cyanide missing from a truck that was hijacked May 10.
Meanwhile, the U.S. Customs Service issued alerts at border posts along the Southwest, said spokesman Jim Michie, speaking to the Dallas Morning News. "We are working closely with Mexican authorities, law enforcement as well as their customs people," he said.
In February, four men linked to al-Qaeda were arrested in Rome with cyanide and city maps. Authorities suspected they planned to poison the U.S. Embassy's water supply, the paper reported.
The Mexican truck was taken about 100 miles north of Mexico City. Trace amounts of sodium cyanide can be deadly when inhaled or ingested. It is used for silver mining and for gas chamber executions.