The South African Police Services are entitled to arrest a person when they become aware of a person contravening a law of the Republic. This typically happens when someone (referred to as a complainant) opens a case against someone else (referred to as the accused), or when a Police officer sees someone contravening the law, such as witnessing someone speeding.
It is however a bit more nuanced than this, as the police services should not necessarily arrest for just any offence. There are various different offences, such as common law offences (murder) and statutory offences (speeding). The Criminal Procedure Act generally dictates when the police can arrest and the procedure the police must follow before, during and or after arrest. Section 56 of the Criminal Procedure Act, read with the relevant proclamations from the Minister, provides that if it comes to arrest, and the police think that an accused, if found guilty, will not pay a fine of more than R 2,500.00, they should not arrest the accused, but should instead provide a written notice for the accused to appear in court. So just because an offence was committed, does not necessarily mean that there MUST be an arrest.
The most often problem encountered in practice is that police officers do not properly identify themselves when asked, even though they MUST show their official identification when it is requested. This is provided for by the section 334(2)(a) of the Criminal Procedure Act.
If the police fail to follow the correct procedures in an arrest, the arrest may amount to an unlawful arrest, and any detainment thereafter may be considered as unlawful. This unlawfulness can go even so far as to translate to malicious prosecution if the National Prosecuting Authority (NPA) proceeds with the charges.
In some instances the police may require to take a blood test, a DNA sample or even require an identity parade to be held. All of these aspects have strict procedures that need to be followed, even when it comes to their reason for doing so or the deadline that they have, such as with taking a blood test or DNA sample. If the procedures are not followed correctly, and the chain of evidence is broken, it may lead to the evidence being declared wholly inadmissible. In this regard, it is better to have an attorney there, someone who knows what to look for, while it is being done, as this will make it easier to have the evidence challenged at a later stage.
Irrespective, when a person is arrested, they must be taken to court within 48 hours for a bail application. If this 48 hours expires on a public holiday or weekend, it will be the next court day thereafter. This means that if a person is arrested on a Thursday or Friday, they can expect to only be taken to a court on the following Monday. So if the police want to speak to you, it is advised that you request to speak with them on a Monday, Tuesday or Wednesday - to prevent from being kept in custody over a weekend.
It goes without saying however that it is strongly advised that, when arrested or questioned by the police, that a person should NOT MAKE ANY STATEMENT without first consulting an attorney. The reason for this is very simply that you will not be told all the particulars of the charge against you, and you may then accidentally incriminate yourself by trying to "help" the police or yourself.