NEW: Napolitano will go to Arizona to talk with fellow officials about the investigation
2 men are being questioned, a source in Mexico's attorney general's office says
They were detained near the U.S. border with drugs and guns, says the source
They are being questioned about the fatal shooting of a U.S. Border Patrol agent
(CNN) -- Two men were being questioned Thursday by Mexican authorities about a shooting that killed a U.S. Border Patrol agent and wounded another near the U.S.-Mexican border in Arizona, a source in the Mexican attorney general's office said.
The Mexican army handed over to local authorities in Sonora two men they had detained near the American border, the source in the federal department said Thursday. The two were in possession of drugs and guns when they were detained, added the source.
Local authorities are investigating if the pair had anything to do with Tuesday's shooting near Naco, Arizona, where Border Patrol agents came under fire after responding to a sensor that had gone off nearby.
U.S. authorities have identified the agent killed as 30-year-old Nicholas Ivie. The Provo, Utah, native, who joined the Border Patrol in January 2008, is survived by his wife and two young children.
Ivie is the 14th agent killed in the line of duty since 2008, including three this year.
He was killed near a border station recently named for Brian Terry, whose 2010 death led to the public disclosure of the botched Fast and Furious gun-smuggling sting, according to Sen. Chuck Grassley of Iowa.
The agent who was wounded has not been identified. After the shooting, he was airlifted to a hospital with non-life-threatening injuries.
He was released from the hospital Wednesday, said Jeremy Copeland, an agent with the Tucson Sector of U.S. Border Patrol.
U.S. Homeland Security Secretary Janet Napolitano will travel Friday to Arizona, along with other federal officials, "to express their condolences" to Ivie's family, according to department spokesman Matt Chandler.
"Napolitano (and the others) will also meet with federal, state and local law enforcement officials at the Brian A. Terry Border Patrol Station in Bisbee, Arizona, regarding the ongoing investigation," Chandler said in a statement.
In addition to Mexican authorities, the FBI is conducting a joint investigation with the Cochise County Sheriff's Office. James Turgal, special agent in charge of the FBI's Phoenix division, has declined to say if the Border Patrol agents involved in the incident returned fire.
As of Wednesday, investigators had not found the weapon used in the shooting, a U.S. law enforcement official said.
Lanny Breuer, assistant attorney general for the Criminal Division of the Justice Department, said earlier this week that investigators were at the scene.
"Every time that a law enforcement person is either killed or shot or injured in the line of duty, we have to take a moment and think of our families and think of the heroes involved," Breuer said.