Michael Jackson -- The Urination Explanation

Finally an explanation as to why Michael Jackson's 1993 accuser could identify the discoloration on the singer's genitals ... Michael liked to pee for an audience.

TMZ has obtained files from the 1993 Santa Barbara molestation investigation. A deputy from the Santa Barbara Sheriff's Department noted the young accuser was able to describe -- in explicit detail -- the discoloration on Jackson's genital area ... the result of Vitiligo, a skin discoloration disorder.

TMZ's Harvey Levin spent 3 hours last Sunday with Dr. Arnold Klein, Jackson's best friend and doctor for decades. Dr. Klein insists Jackson did not molest the boy, and says the reason he could describe Jackson's genitals is because Jackson liked to pee in front of other people. Dr. Klein said Jackson thought it was funny.

Klein says there were numerous times when Jackson would pee in the doctor's home -- in a cup!!! -- around groups of people, including children.

Klein says Jackson would also pee in front of other people in his office.

Dr. Klein says the 1993 accuser saw Jackson peeing and that's why he could identify the genital markings.