The police were summoned by UPS employees who had a package that had been returned by the driver as "addressee unknown." When opened, it was found to contain a large brick of a substance that the UPS testers determined was C4 explosive. After conducting a field test that confirmed that the substance was C4, the police resealed the package and placed it in the "undelivered" section at UPS. They then waited for someone to pick it up. A woman appeared later in the day, claimed the package, and departed. The police followed her to a home known to them to be that of a suspected terrorist. Within minutes after the woman entered the home with the package, the police entered, arrested both the woman and suspected terrorist, and seized the C4. Was this warrantless action lawful?