"Coming in from different angles, that is more than likely how it ended up happening," McCubbin told The Arizona Republic of the shootings.
A Mexican law enforcement official said Thursday that federal police had arrested two men who may have been connected to the shootings. The official, who spoke on condition of anonymity because he was not authorized to release the information, said it was unclear if there was strong evidence linking the men to the case.
Mexican authorities on Friday didn't immediately respond to telephone messages from The Associated Press.
After a meeting of border governors Friday in Albuquerque, N.M., Arizona Gov. Jan Brewer stood by the criticism she leveled earlier this week in response to the shootings in which she said a political stalemate and the federal government's failures have left the border unsecured and Border Patrol agents in harm's way.
"It's the federal government's responsibility to secure our border, and they need to do that, and then we can deal with all the other issues that have come about because our border hasn't been secured," said Brewer, who plans to attend Ivie's funeral Monday in Sierra Vista.
The Border Patrol couldn't immediately comment on the frequency of friendly fire shootings involving its agents. But such incidents appeared to be extremely rare, if they've ever occurred at all.
"I know of absolutely none in the past, and my past goes back to 1968," said Kent Lundgren, chairman of the National Association of Former Border Patrol Officers, citing the year he joined the agency. "I'm not saying it never happened. I'm just saying I've never heard of it."
Also Friday, Homeland Security Secretary Janet Napolitano traveled to Arizona to express her condolences to Ivie's family and meet with authorities. The family did not return calls from The Associated Press on Friday.