Ex-NFL lineman Khalif Barnes -- who had a long stint with the Oakland Raiders -- has been interviewed by police as part of an investigation into the mysterious death of a man in Harris County, Texas.
Here's the backstory ... the body of 29-year-old Jordan Davenport was found in a lake on October 31st.
Cops are looking into tips that Davenport was involved in a violent altercation with several men on Oct. 27th -- the last day he was seen alive.
We're told ... cops received a tip that 36-year-old Barnes may have been involved in the altercation so they tracked him down and spoke with him about the incident.