I can't seem to find the article I recently read to give the citation, but the gist of it was that you need a release always, every time, no exceptions, no excuses....even to photograph the same person on a different occasion. The person interviewed was an attorney who deals with such matters, and he was unshakably adamant. The consequences of not doing so could be financially catastrophic. Perhaps someone else can cite the publication with the interview, but it was bedrock absolute advice.