A law enforcement official said Monday a man suspected of fatally shooting a cattle rancher near the Arizona-Mexico border was a Mexican who was recently in the United States.
Some politicians have said the attack is evidence that border security must be strengthened.
The official said it's not known if the suspect was still in the U.S. and noted the person who killed rancher Robert Krentz more than a month ago wasn't believed to be a U.S. citizen.
The person works for an agency that isn't leading the investigation and requested anonymity.
Carol Capas, spokeswoman for the Cochise County Sheriff's Office, which is leading the investigation, declined to confirm the account.
Krentz was on his all-terrain vehicle checking water lines and fencing when he was shot March 27 on his 35,000-acre ranch northeast of Douglas, Ariz. The wounded rancher managed to speed away before he lost consciousness and died.
At a congressional hearing last month, Cochise County Sheriff Larry Dever said the rancher was believed to have been killed by an illegal immigrant who was headed to Mexico and worked as a scout for drug smugglers.
Scouts generally serve as mountaintop lookouts for drug smugglers, instructing the drivers for smuggling rings to pull over and hide when authorities are nearby.
Arizona passed a new law last month requiring local and state law enforcement officers to question people about their immigration status if there's reason to suspect they're in the country illegally.