The technique relies on what's known as a split-time lens to create a temporal hole. A beam of light is pushed through the lens, which speeds up the travel of the fast moving blue light, and slows down the comparatively sluggish red, leaving a gap in the middle — a gap ripe for exploitation. The light is recombined on the other side, and for a window of trillionths of a second, whatever goes on in that gap is undetectable.
Whatever's in the gap should interact with the light passing through, but it simply...doesn't. The travelling light beam emerges on the other end of the lens unscathed and untouched, completely oblivious to what happened in that undetected picosecond gap.
So far, the technique only works on periods of 0.00012 of a second - so the police can probably rest easy, as evildoers would have to move far faster than human beings ever could to 'conceal' their actions.
Instead, the 'hidden' fractions of a second could be used for ultra-secure communications.The scientists think that the technique could even be combined with recent advances in optical 'cloaking' - to hide an event in both space and time.