In what circumstances will a police officer leave a suspect in the back seat of a patrol vehicle with the motor running?

In Duarte v. City of San Jose, supra, 100 Cal.App.3d 648, 161 Cal.Rptr. 140, a police officer arrested a suspect for driving under the influence of alcohol and left him, unattended and unhandcuffed, in the back seat of a patrol vehicle with the motor running. The suspect got into the driver's seat of the patrol vehicle and sped off. A high speed chase ensued, which ended when the suspect drove into the front yard of the plaintiff's residence, striking and seriously injuring the plaintiff.