Updated

PHARR, Texas -- A couple of American missionaries who were shot at in Mexico may have been targeted because they were driving an expensive truck, police said Thursday.

Nancy Davis, 59, was hit in the head and died in a Texas hospital Wednesday afternoon, about 90 minutes after the two were shot at in Mexico. Her husband described a frantic scene in which he sped toward the border desperately driving against traffic over a bridge that connects Mexico to the United States, according to a police statement.

The police chief in the border city of Pharr, Ruben Villescas, said pickups such as the 2008 Chevrolet belonging to Nancy and Sam Davis are coveted by criminal organizations in Mexico, and damage to the truck suggests that another vehicle tried to run them off the road.

Police said the couple are missionaries from Texas who travel extensively into Mexico.

The scene echoed one described four months ago by an American tourist, who said her husband was gunned down by Mexican pirates on a border lake as the couple tried to flee on Jet Skis.

"I don't know them, but my heart breaks for them," said Tiffany Hartley, the widow of David Hartley, who authorities say was killed on Falcon Lake in September.

Sam Davis told investigators he and his wife were traveling about 70 miles (113 kilometers) south of the Mexican border city of Reynosa when gunmen in a pickup tried to stop them. When the Davises accelerated, the gunmen fired, wounding Nancy Davis in the head, the statement said.

Police said Davis told officers he continued to drive at top speed in hopes of outrunning the gunmen until he reached the Pharr International Bridge and sought help.

Villescas said Mexican authorities contacted by his department confirmed the shooting happened near the outskirts of San Fernando south of Reynosa. The area is heavily controlled by the Zetas drug cartel and is one of Mexico's most dangerous. It is the same area where 72 Central and South American migrants were found slain in August, a massacre that was blamed on the Zetas.

Pharr police and U.S. Customs and Border Protection agents converged on the couple's truck just before 12:30 p.m. Wednesday, after Sam Davis stopped in the middle of bridge traffic to seek help. Nancy Davis was found bleeding from a head wound in the front passenger seat. She was pronounced dead an hour-and-a-half later at an area hospital, according to the police statement.

The police statement did not include details of the couple's missionary work, and the police chief did not immediately respond to requests for comment late Wednesday.

A friend of the couple said the two spent 80 percent to 90 percent of their time in Mexico and had a home in the Mexican state of Nuevo Leon. The rest of the time they were in Texas and traveling across the U.S. raising funds for Gospel Proclaimers, the organization they founded.

"They've been working in Mexico for over 30 years," Merton Rundell III, the director of finance at Union Bible College in Indiana, told The Associated Press on Thursday. "It was mainly establishing churches -- that was their main thrust.
The Mexican Interior Ministry released a statement expressing condolences over Davis' death. It said Mexican authorities were investigating.

Concerns about the investigation into David Hartley's death led Texas Gov. Rick Perry to call for a stronger response from Mexican authorities. His body was never found, and a Tamaulipas state police commander who was investigating was killed and his decapitated head delivered in a suitcase to a local Mexican army post.

On Thursday, Perry's spokeswoman, Katherine Cesinger, said Nancy Davis' slaying underscores the need for greater border security.

"How many Americans are going to have to die for the federal government to pay attention and realize they need to secure the border," she said.

In the migrant massacre, a state detective and local police chief who participated in the initial investigation were killed.