The purpose of the 4th Amendment is to prevent the creation of a police state in which the government can simply go around randomly searching people’s property and persons in an attempt to find criminals. The 4th Amendment ensures that the government has to have a good reason before it can invade our privacy in search of evidence of wrongdoing.
The 4th Amendment protects criminal suspects because it forces the police to have a good reason, as determined by a judge, to search the suspects’ property or their persons. If it were not for the 4th Amendment, the police might have the power to simply search any person or place that they wanted to search without having any good reason. They could come up to your door and require you to let them search your house even if you had not given them any reason to think you had done wrong. This protects criminal suspects because it forces the police to have probable cause to search them or their property. It prevents the police from conducting searches or seizures just because they are suspicious of the person in question.