Agent Robert Rosas was killed during an attempted robbery in the mountains east of San Diego in 2009.
The FBI provided police in Tijuana with information that led to the arrest of 26-year-old Marcos Manuel Rodriguez Perez. He is believed to be one of three men involved with Rosas' slaying.
A 17-year-old Mexican national has already been sentenced to 40 years in prison for his role in the killing.
