I just saw this, thought I'll give it a go. I hardly do any 'whodunnit' type horaries, so not sure of this...Also I don't listen to rap, so don't know much about this guy at all.
If I take Biggie to be Mercury, 1st ruler. He is right on MC, in gemeni, retrograde and combust. Being in its own domicile and conjunct MC, very descriptive - this man was well known, at the height of his career, with lots of talents. Mercury is exceptionally well dignified both accidentally and essentially. But then we have this combustion and retrograde, things were not so good obviously. Sun is inflicting pressure on Mercury, Sun in Gemeni - several men, young as well, being Gemeni. But Sun and Mercury have power over each other - Mercury actually rules Sun, Sun combusts Mercury. There is some sort of ongoing relationship. Mercury is retrograding back towards Sun, its almost like it was trying to move away from Sun but now turning back to Sun. Perhaps trying to fix things with whoever Sun is. There is also Venus here, a woman involved. So to me it looks like Mercury had some sort of professional relationship with the Sun people, mutually benefiting relationship. But Mercury is slightly weaker, being RX and it getting closer to the Sun. Sun has more power here essentially.
If Mars is the act itself, its in the 12th. Sun rules Mars, and just separating from Mars. So I think whoever Mars is, Mars is the gunman, hired by Sun.
Saturn on ASC makes me think Biggie felt burdened, there is a heavy load here. Some great responsibility on his shoulders. He definitely was feeling some pressure and perhaps knew something was not going well. So I think Biggie was gunned down by someone who is unknown, but hired by Sun, who he knew and felt comfortable with (Sun in Mercury's domicile). Sun is interested in the work of Mercury and most likely something went wrong. This might also have to do with a woman. OR the people who tried to control Biggie was a couple.
Just my take. I'm probably wrong, I will have to do some research and maybe try interpreting again another time.
Just my take.