Final answer:
To frisk a suspect, the police need reasonable suspicion that the individual is involved in criminal activity and may be armed and dangerous. This standard, established by the Supreme Court, is less than the probable cause required for search warrants. Warrantless searches can occur under specific conditions, such as with consent or in exigent circumstances.
Step-by-step explanation:
The condition that allows for frisking a suspect is suspicion. This is in line with the precedent set by Terry v. Ohio, where the U.S. Supreme Court ruled that police may stop and frisk a suspect if they have reasonable suspicion that the person is involved in criminal activity and may be armed and dangerous. This is considered sufficiently less than probable cause, which is necessary for obtaining search warrants or establishing strong evidence before the involved individual's trial. The courts have also set forth that this reasonable suspicion must be based on specific and articulable facts, rather than mere hunches.
In the scenario where police apprehend individuals suspected of an armed robbery, they may frisk the suspects if they have reasonable suspicion that the suspects are carrying weapons. In contrast, for more intrusive searches, like those involving entering homes or vehicles, police usually require a warrant, unless exigent circumstances exist. Moreover, warrantless searches can be conducted based on consent, when evidence is in plain view, or when there is an immediate threat of evidence destruction.
Probable cause is a lower threshold than what is needed to convict at trial, and, according to Illinois v. Gates, it should be determined under the 'totality of circumstances' test. This balancing act between individual rights and law enforcement needs reflects the ongoing debate over the Fourth Amendment's protection against unreasonable searches and seizures.