For stamina, I would look into
interval training, whether it be applied to running, swimming, cycling, rope skipping, etc.Ideally, you should apply it to running as most law enforcement agenices have a timed run as part of their application process.
Running intervals at a track is an excellent way to get into shape and as it is primarily anaerobic(sprint-like)in nature, it will better prepare you for the demands of a law enforecment occupation.400-800m distances are best with a limited rest interval between each repeat.
You should also focus on strength-endurance, primarily by implementing some calisthenics into your routine.Pull-ups should be one of your primary exercises as it is very "functional" in regards to some of the demands of a LEO.Push-ups, sit-ups, squats, and back extensions should also be included.Burpees(a squat thrust followed by a vertical jump) are excellent for developing strength and power in the legs and hips as well as being a terrific conditioning exercise.
As for suppleness, implementation of a sound flexibility program following your exercise session should be fine.