Ask HN: Arguments and sources supporting open-source for tax-funded software?

I am trying to find some reliable sources substantiating the societal benefits for governments developing their software openly, especially when funded by public spending. It is also relevant, but slightly less so, to find evidence (if there is any) indicating the benefits of using open systems such as Linux as opposed to proprietary systems in the public sector. I have looked at Bulgaria as an example for developing systems openly and Munich/Vietnam as examples for using non-proprietary systems but I can only find news coverage and I want tangible data supporting the respective benefits. Any arguments that you yourself might have that are pro- or against open-source and open systems within the government are also appreciated.