Under what condition can police search a passenger's belongings in a vehicle?

The ability for police to search a passenger's belongings in a vehicle hinges on the principle of probable cause. When law enforcement officers have probable cause to believe that the belongings contain evidence of a crime, they are legally permitted to search those items without a warrant. This standard is based on the notion that the officers have reasonable grounds to suspect that criminal evidence is present, which provides them the authority to conduct the search to preserve that evidence and maintain public safety.

While other conditions might allow for searches, such as having a warrant or receiving consent from the passenger or driver, these specific scenarios do not directly pertain to the necessity and sufficiency of probable cause as a basis for searching a passenger's belongings. Hence, it is the existence of probable cause that allows officers to act without needing further permissions in this specific context.