I shall present the theory in full detail, but looking at the facts of Tupac calling Dr. Dre gay, Dr. Dre being on his way out the door in the record company... it all just seems to stem from eliminating all competition. 50 cent was shot, almost dead, then left Columbia to "join" Dr. Dre's company... Also, Dr. Dre releases albums soon after the killings/attempted killings 
(as if it were some inspiration). For instance, the lyrics here ( https://genius.com/Dr-dre-murder-ink-lyrics ) speaks to me as if he his talking about 50 cent. Then the Aftermath lyrics of Crown the Empire after the killing of Tupac...
This is the basics, again, I will present more evidence to elaborate on the theory. Stay tuned.
Oh, the killings were way of orders, hypothetically. I suspect that he ordered to kill Shug Knight recently also. So again, attempted killings/killings by orders theory/theme.