Complex sentence: Cantu and Garza were carrying a rifle, which they used to rob the two men of their wristwatches, and tried to take their cash, but were interrupted by Gomez's attempt to retrieve a pistol hidden under his mattress.
Split into simpler sentences: Cantu and Garza were carrying a rifle, which they used to rob the two men of their wristwatches. As they tried to take their cash, they were interrupted by Gomez's attempt to retrieve a pistol hidden under his mattress.