Does "all found to have contained incriminating videos" cause sentence to be incomplete? so,

The sentence is correct as it is:

"The collection consisted of pliers, screwdrivers and hammers, all discarded by the striking workers."

(I would prefer a comma after "screwdrivers" – Oxford comma – but it's not strictly necessary. Note how often you see it being used and you can decide whether or not to use it yourself.)