1. The United States Supreme Court has held that normally, a police seizure of either evidence of a crime in a constitutionally protected area or a possible criminal defendant must be based on probable cause e.g., Illinois v. Gates 1983. Furthermore, the Court has repeatedly stated that a government search or seizure on private premises without a warrant is presumptively unreasonable under the Fourth Amendment unless it falls within one of the "carefully delineated" Welsh v. Wisconsin, 1984 exceptions to the Fourth Amendment warrant clause. Strong policy interests in preventing possible abuse by government agents support the Court"s insistence...
frown upon incomplete or poorly conducted investigations, due to the risk of ignoring potentially exculpatory evidence. Courts also have prescribed that police officers must be "thorough" . It is well established that once probable cause exists, there is no duty to investigate further. Additionally, officers must "reasonably interview witnesses readily available at the scene" of the crime. Therefore, in our case an officer should analyze evidence for probable cause by interviewing Mr. A who is probably a witness and checking Mr. B's alibi. After that an officer can decide whether there is probable cause to search or to arrest.