CHULA VISTA, Calif. (AP) - Mexican police announced the arrests Saturday of four men suspected of involvement in the killing of a U.S. Border Patrol agent as American investigators searched hospitals for gunmen who were possibly wounded in the first such shooting death in more than a decade.
Investigators said they have notified hospitals on both sides of the border to be alert for patients with suspicious or unexplained injuries. They said at least two people may have been wounded and left blood at the scene.
Agent Robert Rosas was killed while responding alone to a suspected border incursion near Campo, a town in rugged, arid terrain in southeastern San Diego County. He was shot in the head and body and was dead when other agents arrived, said Keith Slotter, special agent in charge of the FBI's San Diego bureau.
The men detained in Mexico are allegedly part of an immigrant smuggling ring, and 21 immigrants were found with them when police detained them and seized four guns near Tecate, said Elias Alvarez Hernandez, coordinator of federal police in Baja California state.
Alvarez also said at the news conference that one of the suspects claimed in conversations with police that another man detained Friday with a handgun had shot Rosas.
But FBI spokesman Darrell Foxworth told The Associated Press in a brief email Saturday night that he could not confirm or comment on any arrest reports. The bureau did not return phone calls left throughout the day.
Mexico police did not say what evidence they had against the four, whom they identified as Jose Quintero Ruiz, 43, and his brother Jose Eugenio Quintero Ruiz, 49, and taxi drivers Jose Alfredo Camacho, 34 and Antonio Valladares, 57.
American officials have expressed concerns that the drug cartel battles plaguing Mexico could spill into the United States with the targeting of U.S. law enforcement officials. Slotter said investigators aren't ruling out the possibility that Rosas was slain by drug smugglers or even human smugglers.
Arturo Sarukhan, the Mexican ambassador to the United States, said Mexican law enforcement agencies are cooperating in the case.
"This is a tragic example of the violence we keep facing at our common border as President (Felipe) Calderon continues to roll back transnational organized crime, and underscores the need for both our countries to keep working as full partners to guarantee the safety and security of those living on both sides of our border communities," Sarukhan said in a written statement Saturday.
Investigators said blood evidence at the scene indicated at least one culprit and possibly others had serious injuries, perhaps by gunfire. They didn't know how many shots were fired, if Rosas fired any shots himself, or how many guns were used.
"It's all possible. I can't definitively say X number of people fired or Agent Rosas got off shots or didn't. I mean, it's too early in the investigation to say that with any certainty," Slotter said.
Authorities said at least one other agent in the field heard gunshots after Rosas left to respond to the call, and Rosas couldn't be reached on his radio afterward.
Rosas was the first Border Patrol agent to die in a shooting in more than a decade, according to The Officer Down Memorial Page Inc., which tracks fallen officers using information provided by law enforcement agencies. Another agent, Luis Aguilar, was intentionally run over by a fleeing man driving a drug-laden Hummer in January 2008.
Rosas, a three-year Border Patrol veteran, had a 2-year-old son and an 11-month-old daughter, said Richard Barlow, acting chief patrol agent for the Border Patrol's San Diego sector.
Authorities could not confirm reports that he called for backup and then went ahead before anyone arrived, but said it isn't unusual for agents to work alone along the border.
Since 1919, 108 Border Patrol agents have died on duty, according to The Officer Down Memorial Page. Gunfire was the leading cause with 30 deaths, followed by automobile accidents and aircraft accidents.
The FBI is offering a $100,000 reward for information that leads to the arrest and conviction of the killer or killers.
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Stevenson reported from Mexico City. Associated Press writers Christina Hoag in Los Angeles and Amy Taxin in Long Beach contributed to this report.
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On the Net:
The Officer Down Memorial Page Inc.: http://www.odmp.org