Foggy/rainy weather had limited visibility, but the skies cleared May 3. A USGS overflight revealed the crater was completely drained:
At 10:30 AM, a magnitude-5 earthquake caused more of the crater to collapse, throwing up a cloud of pink ash.
Pu’u O’o crater sends up cloud of ash after M5.0 earthquake. HVO Photo/Video blog. Again, Full-sized image is dramatic.
See also Mick Kalber’s May 2 flyover video.
Meanwhile, increased seismicity at the summit coincided with the summit lava lake changing from inflation to deflation— this is when it began to drop (source: HVO Volcano Watch).