Many police ‘ powers, privileges, duties and responsibilities’ are prescribed in the Summary Offences Act 1953 (SA). In addition, numerous Acts and common law principles provide for other police powers [see Summary Offences Act 1953 (SA) s 82 ]. The following discussion of general police powers relates to the investigation of suspected crimes including the power of arrest, powers to search premises, vessels, vehicles and people, and to seize property.
The requirement there is “reasonable cause to suspect” precedes the use of many police powers and provides validity to subsequent police action. When legislation requires "reasonable grounds" as a state of mind (including suspicion and belief), it requires facts ‘ sufficient to induce that state of mind in a reasonable person ’. In relation to a suspicion, ‘[t]he facts which can reasonably ground a suspicion may be quite insufficient reasonably to ground a belief, yet some factual basis for the suspicion must be shown’ [see George v Rockett  170 CLR 104at 112 and 115;  HCA 26]. Suspicion is a state of mind which ‘ falls short of belief ’ [see Homes v Thorpe  SASR 286 at 291] and ‘ is more than mere idle wondering whether [the situation]... exists or not ’ [see Queensland Bacon Pty v Rees  115 CLR 266 at 303;  HCA 21]. This principle requires some substance to the suspicion (beyond a hunch) for the establishment of “reasonable cause”.
The police have extensive powers to investigate suspected criminal offences. They can search premises, vehicles and vessels (ships and boats), and seize property when:
- a person consents to the search of their property; or
- the police have a valid search warrant (issued under various Acts and some requiring court authorisation); or
- without a warrant, where the police have reasonable cause to suspect stolen goods or evidence of the commission of an offence.