A massive police presence descended upon Omar Mateen 's Florida family home Sunday afternoon, hours after authorities ID'd him as the killer in the Orlando nightclub massacre ... and TMZ has obtained the first photos showing police combing the property for clues.

Cops -- some of them wearing leather gloves -- can be seen searching the trunk of a Mercedes SLK 230 and loading numerous boxes into police vehicles. Check out the photos ... you also see police speaking with Omar's father, Seddique.