Investigate Threatening Letter

I'm seeking a professional to help identify who googled my address and sent a threatening letter. The letter was written using red marker.

Key Requirements:
- Experience in investigations or tracing individuals
- Ability to handle sensitive information discreetly
- Skills in online research and data gathering

Ideal Skills and Experience:
- Background in law enforcement or private investigation
- Proficiency in cybersecurity and online privacy tools
- Strong analytical skills to evaluate potential suspects

Please provide a detailed plan on how you would approach this task.