Alfonso Hoffman raised his right hand and swore an oath Wednesday -- to uphold the laws of the state and county and perform the duties of a K-9 deputy sheriff of the Transit Policing Division.
After being fitted with a green tactical vest and handed a leash, Alfonso climbed into an armored truck for his first patrol.
The 12-year-old kid crime-fighter, diagnosed with leukemia this year, got a chance to live his dream on Wednesday, joining a Los Angeles County Sheriff's Department K-9 patrol.
Read more from NBC Southern California.
Follow NBC News Latino onFacebook, Twitter and Instagram.