Floyd Mayweather Tells Cops ... I Heard the Murder/Suicide

Floyd Mayweather finally sat down with the LAPD for a 2-hour interview Wednesday, telling detectives he desperately tried talking his good friend, rapper Earl Hayes, out of killing himself.

Law enforcement sources tell TMZ ... Floyd confirmed the story first reported on TMZ ... that he was on FaceTime Monday morning with Hayes when the rapper walked away from the phone, into the bathroom and pumped multiple bullets into his wife, Stephanie Moseley.

Floyd told detectives after Hayes shot his wife, he came back to the phone and continued talking with Floyd. The boxer says Hayes said he was going to shoot himself and Mayweather pleaded with him ... to no avail.

As for what happened before shots rang out ... Mayweather acknowledged he was talking with Hayes about Stephanie's infidelity, but denies riling the rapper up.

Detectives asked Floyd why Hayes called him at 7 AM. Mayweather said it was because they were best friends and Hayes was trying to say goodbye.