Final answer:
The seizure of the man and the subsequent search appear to be lawful under the Fourth Amendment. The drugs and the gun may be admissible in court as evidence.
Step-by-step explanation:
Based on the information provided, the seizure of the man and the subsequent search appear to be lawful under the Fourth Amendment of the United States Constitution. In the landmark case of Terry v. Ohio, the Supreme Court ruled that police officers have the authority to stop and frisk individuals if they have a reasonable suspicion that the person is armed and dangerous. In this scenario, the officer approached the man on the street corner and believed he was selling drugs, which would give rise to a reasonable suspicion of criminal activity.
Additionally, during the frisk, the officer discovered a concealed handgun. This discovery further validated the officer's suspicion that the man was armed and potentially dangerous. It is important to note that the officer's actions were within the bounds of the Fourth Amendment because they were based on reasonable suspicion.
Furthermore, during a search incident to arrest, the officer found six grams of heroin in the man's coat pocket. This evidence is likely admissible in court, as it was discovered during a lawful arrest and search incident to that arrest. The handgun, being a stolen item, may also be admissible in court as evidence of a separate crime.