They could go 'all honest' - and say...
"Dear Backers: We have been let down by a trusted member of the Batteroo engineering team, who has been identified - and now left the company (with entitlements). His motives were ill-formed, and distracted by the hacker/developer community. We have to blame someone, and this (someone) has let us all down."
"We regret that due to invalid research metrics, and data produced by this team member, Batteroo are unable to proceed with the Batteriser project. This is a disappointing end to this project which was on track to save the planet, run 'Big Battery' into the ground, and feed starving children across the globe."
TRANSLATED: We have collected enough money, (someone) has resigned from the company, and we're all off to the beach.... and my dog died (after eating the schematics).