I'm an investigative journalist working on a story about corporate fraud, and I need to verify information from confidential sources without compromising their safety. What are the most effective methods for balancing source protection with factual accuracy?

I've received tips from insiders about financial misconduct in a large company, but the sources fear retaliation if their identities are revealed. I want to ensure the data is accurate for publication while adhering to ethical journalism standards. I've started by checking public financial reports, but some discrepancies aren't documented there. What specific steps should I take to build a credible case?