NACO, Ariz. (AP) — Investigators were scouring a rugged area near the U.S.-Mexico line looking for evidence in the fatal shooting of a Border Patrol agent.?Nicholas Ivie and a colleague were on patrol in the desert near Naco, about 100 miles from Tucson, when gunfire broke out shortly before 2 a.m. Tuesday, according to the Border Patrol.?Ivie, 30, was killed. The other agent, whose name hasn't been released, was released from the hospital after being shot in the ankle and buttocks.?It was the first fatal shooting of an agent since a deadly 2010 firefight with Mexican bandits that spawned congressional probes of a botched government gun-smuggling investigation.?No arrests have been made. Authorities suspect that more than one person fired at the agents.?No weapons have been found, according to a federal law enforcement official who spoke on the condition of anonymity. The official requested anonymity because information on the search hasn't been publicly released.?Agents and deputies were searching the area on ATVs, horseback and on foot with up to four helicopters overhead in the southern foothills of the Mule Mountains that's considered a known smuggling area.?"It's been a long day for us but it's been longer for no one more than a wife whose husband is not coming home. It's been longer for two children whose father is not coming home, and that is what is going to strengthen our resolve" to find those responsible and enforce the law, said Jeffrey Self, commander of Customs and Border Protection's Arizona joint field command.?Ivie lived in Sierra Vista with his wife and their two young daughters.?President Barack Obama called Ivie's family Tuesday to offer condolences and to express his gratitude for Ivie's "selfless service to his nation," a White House statement said.?Obama made it clear that the administration "was doing everything it could to locate those responsible."?The last Border Patrol agent fatally shot on duty was Brian Terry, who died in a shootout with bandits near the border in December 2010. The Border Patrol station in Naco, where the two agents shot Tuesday were stationed, was recently named after Terry.?Terry's shooting was later linked to the government's "Fast and Furious" gun-smuggling operation, which allowed people suspected of illegally buying guns for others to walk away from gun shops with weapons, rather than be arrested.?Authorities intended to track the guns into Mexico. Two rifles found at the scene of Terry's shooting were bought by a member of the gun-smuggling ring being investigated.?Critics of the operation say any shooting along the border now raises the specter that those illegal weapons are still being used in border violence.?"There's no way to know at this point how the agent was killed, but because of Operation Fast and Furious, we'll wonder for years if the guns used in any killing along the border were part of an ill-advised gun-walking strategy," Republican Sen. Chuck Grassley said in a statement.?The Terry family said that the shooting was a "graphic reminder of the inherent dangers that threaten the safety of those who live and work near the border."?Authorities set up a checkpoint on a dirt road about seven miles southeast of Bisbee. Border Patrol agents at the checkpoint declined to comment and barred reporters from going further.?The area near the shooting is scattered with houses, trailers and ranchettes. Mesquite trees and creosote bushes dot the landscape, with a mountain range nearby to the west.?The U.S. government has put thousands of sensors along the border that, when tripped, alert dispatchers that they should send agents to a particular location.?The agents were fired upon in a rugged hilly area about five miles north of the border as they responded to an alarm that was triggered on one of the sensors, said sheriff's spokeswoman Carol Capas. It wasn't immediately known whether the agents returned fire, she said.?The agents who were shot were on patrol with a third agent, who was not harmed, said George McCubbin, president of the National Border Patrol Council, a union representing about 17,000 border patrol agents.?The Border Patrol said Ivie worked for the agency since January 2008 and grew up in Provo, Utah. He worked as an emergency medical technician before joining the Border Patrol, said his brother-in-law, Todd Davis. He served a two-year mission with The Church of Jesus Christ of Latter-day Saints in Mexico City after high school.?Davis said Ivie's desire to help others, and his love of the outdoors and riding horses led him to the Border Patrol, where he served on the horse patrol unit.?"Nick always tried to help others. He was a very selfless man with his family, with his friends, in anything he did," Davis said. "You know the risk but you pray this day would never happen."?Twenty-six Border Patrol agents have died in the line of duty since 2002. Bisbee-area residents expressed a mix of concern and frustration about the shooting, along with recognition that the border can be a dangerous place.?The region has seen its share of violence in recent years, including the Terry shooting and the slaying of a well-known rancher in 2010. That killing was, in part, credited with pushing Arizona lawmakers to pass a law that requires officers, when they stop someone, to check the immigration status of those they suspect are in the country illegally.?"There is no security on the border — none," said Edward L. Thomas, who owns rental properties in Bisbee.