Job Interview Questions: Is it OK to ask for job interview feedback?

I had an interview for a city government job in USA. twelve people were interviewed and I was one of the final three candidates. They even contacted my references.
I never got the job :(
I emailed the main interviewer thanking him for the opportunity and also asked for feedback on my interview. I heard nothing back.
Should I email again or maybe ask the HR department?

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Recommended Answer:
You could follow-up in one of three ways, either by phone, email, or with a thank you letter and express interest in knowing what qualifications in which you were lacking stating it would be valuable to know this for future reference.

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