Police may seize evidence in plain view without a warrant. According to the Supreme Judicial Court (SJC):
Under our plain view doctrine, a police officer may seize objects in plain view where four requirements are met: (1) the officer is lawfully in a position to view the object;
(2) the officer has a lawful right of access to the object;
(3) with respect to contraband, weapons, or other items illegally possessed, where the incriminating character of the object is immediately apparent or, with respect to other types of evidence (‘mere evidence’), where the particular evidence is plausibly related to criminal activity of which the police are already aware; and
(4) the officer “come[s] across the object inadvertently.
Commonwealth v. White, 469 Mass. 96, 102 (2014). Citations and quotations omitted.
Officers frequently use flashlights to illuminate areas that cannot be seen with the naked eye. The classic example is an officer who stops a motor vehicle at night. The officer cannot see directly into the car. He therefore uses his high-powered flashlight to peer into the vehicle. If he sees contraband inside the car with the aid of his flashlight such evidence may be rightfully seized without a warrant pursuant to the plain view doctrine.
Again quoting the SJC,
the use of a flashlight to peer through a window is permissible so long as the police officer was rightfully in a position to make his observations. Since it would not constitute a search for the officer to observe objects in plain view in the automobile in daylight, it ought not to constitute a search for him to flash a light in the car as he was walking past it in the night season. The use of artificial means to illuminate a darkened area simply does not constitute a search, and thus triggers no Fourth Amendment protection.
Commonwealth v. Sergienko, 399 Mass. 291, 295 (1987). Citations and quotations omitted.