Smokey Robinson Investigated for Alleged Sexual Assault in 2015, Wasn't Charged

2:50 PM PT -- Attorneys John Harris and Herbert Hayden, who represent Jane Does 1-4 in the current lawsuit, tell TMZ ... "The statement released by the Los Angeles County District Attorney’s Office confirms that charges were not filed against Mr. Robinson due to insufficient evidence—not because the claims lacked merit. This underscores the significant challenges victims face when reporting incidents of sexual assault, particularly when the alleged perpetrator is a powerful and well-known figure."

They continue ... "Moreover, this latest development further affirms that at least five women have now come forward with allegations of sexual assault against Mr. Robinson. Together, they are united in their pursuit of justice."

Prosecutors in Los Angeles are revealing for the first time Smokey Robinson was investigated for an alleged sexual assault back in 2015 ... but the probe did not result in criminal charges.

The L.A. County District Attorney's Office tells TMZ ... they discovered that in 2015 the D.A.'s office was presented with a sexual assault allegation against Smokey, and that the case was kicked up to prosecutors by the Los Angeles County Sheriff's Department.

The D.A. says prosecutors ultimately decided not to charge Smokey with a crime due to a lack of evidence.

Our sources say the alleged victim from the 2015 sexual assault case is NOT one of the four anonymous women who recently sued Smokey for sexual battery, assault, false imprisonment and gender violence.

Three of the 4 women from the new lawsuit filed police reports against Smokey, and he's now the subject of a new LASD investigation.

Smokey's denied the new claims, called them a shakedown, and has filed a counter suit.

Robinson's attorney Christopher Frost tells TMZ ... "We are pleased that this statement has been released in which the LA District Attorney has confirmed there was no basis to file charges a decade ago."