If the police have placed your patient in custody, arrested them or if the patient is currently in handcuffs, a police officer must ride with you in the back of the ambulance to the hospital. This includes patients that are not being arrested but have been handcuffed for their safety or yours.
While the patient may be calm or non-violent, the police officer must monitor the patient directly while detained (per their policies). They are not permitted to simply follow behind and/or provide you with a handcuff key just in case something happens.
If you have a situation where the officer has handcuffed your patient and indicates they will follow behind, you should advise them that you are not allowed to transport without an officer in the back since the patient is in their custody. You should contact an EMS supervisor for assistance if the officer will not ride.