Light streaks usually occur when a bright light source moves during an exposure, or when the camera itself moves slightly while a point of light is in view. Because investigations often take place in darkness, cameras compensate by using slower shutter speeds. That longer exposure time creates the perfect conditions for streaks, even when the movement is barely noticeable.38One common scenario is the accidental recording of flashlights, phone screens, LEDs on equipment, or car headlights far in the distance. Even a distant light can leave a heavy trail if the camera is handheld. On a long exposure, the slightest twitch of your wrist will drag that point of light across the frame, sometimes creating smooth lines and sometimes jagged shapes depending on how the camera moved.

These streaks can also curve, loop or appear to "change direction" because the camera's movement is interpreted as the light's movement. In a pitch-black location,...