The HPD headquarters building that we saw on Hawaii Five-0 was, in fact, a former Sears store. These pictures tell the tale:
The real-life HPD headquarters building is located on S. Beretania Street, a few blocks from the state capitol building. A museum there includes a salute to Hawaii Five-0 and, especially, Kam Fong, who was a real-life HPD officer for many years.
The Sears building. Notice the design on the upper portion of the front.
Here's an interior shot. The escalators are left over from the store, although the sales space has been closed in to form offices as evidenced by the fact that the walls do not reach the ceiling. It is entirely possible that the walls are "set" walls and that the space really is still open store space.
Hats off to Elliot Street. His appearances in "The Grandstand Play" (Season 3) and "Draw Me a Killer" were outstanding! I feel a special closeness to him, for he hails from my dad's hometown, Meridian, Mississippi. There, he was active in helping to restore and preserve the city's opera house. Bravo!