Reddit reviews Cyber Crime and Cyber Terrorism Investigator's Handbook

Yes, most Gov jobs require at least Sec+.

Depending on how much you did as an LEO you may look into computer forensics. Network Security etc. You may also want to beef up knowledge of networking as well. So either the Net+ and/or CCNE cert.

Books are always a good place to start. I don't know about this one but have read a few other books by this publisher that have been pretty good.

Ones I have read/skimmed:

• Social Enginnering Penetration Testing
  
• The Basics of Inormation Security: Understanding the Fundamentals of InfoSec in theory and Practice
  
• The Basics of Hacking and Penetration Testing
  
  
  Haven't picked this one up myself, but it has good reviews
  
  
• RTFM: Red Team Field Manual
  
• The Hacker Playbook