Michael Jackson Surveillance Video Erased

3/16/2011 7:30 AM PDT

Michael Jackson Surveillance Video Erased

The surveillance video of Michael Jackson's home the day he died has been erased -- lost forever, because the LAPD never knew MJ's death would turn into a criminal case.

TMZ broke the story ... the LAPD only copied 4 minutes of footage from the surveillance videos trained on Michael's house the day he died.  The video shows Jackson coming home from rehearsal at around 12:30 AM. 

Dr. Conrad Murray's lawyers will ask a judge today to order authorities to turn over the nearly 24 hours of surveillance video surrounding MJ's death.

But here's what we found out.  The tape recirculates every 24 hours, and when the LAPD pulled the video shortly after MJ's death, the case was not a homicide investigation so all cops wanted to do was establish a time line -- so the only relevance of the video was showing when MJ entered the home.

We're told cops never looked at the rest of the surveillance video.

The video would have shown who entered the house and when, on the day MJ died.  It will now and forever remain a mystery.