In a supplement to an earlier comment, the commenter describes noticing white waxy and darker substances …

I wanted to add this to a comment I have already submitted... This occurred to make earlier today. His hands were definitely clean. Less than 5 minutes before taking these pictures he had washed his hands with dawn detergent. While working on a project he had needed to scrub a metal lock mount with dawn soap so he could attach components to the bare metal surface. While waiting for the piece to fully dry so he could rinse the surface with alcohol, he sat down by his laptop and work area. He had left an omnidrection microphone (pictured) on the desk. He opened the static bag, set it down for a minute or two by his other components and then wanted to see the part number on the component. Using his phone's zoom he looked at the component and noticed the white waxy substance I alluded to in my report as well as some darker substance.