Complex sentence: Several years later, he was admitted to the federal police led by the office Attorney General of Mexico and was stationed at Nuevo Laredo and then Reynosa, Tamaulipas, where he worked until 1996, when he established a business relationship with the Juárez Cartel.
Split into simpler sentences: Several years later, he was admitted to the Federal Police, which is led by the office Attorney General of Mexico and was stationed at Nuevo Laredo. He was then stationed at Reynosa, Tamaulipas, where he worked until 1996, when he established a business relationship with the Juárez Cartel.