Same people that killed Michael Jackson. Tupac, like Michael Jackson was getting too famous and too big not only here, but internationally as well. They were influential with their poetry, they inspired millions of people around the world.
I believe that government/CIA felt threatened by Tupac, because he was speaking out against social injustice, racism, and government control. And he was influencing his fans around the world, he basically became too big and too influential. Tupac hated cops, he even shot two undercover police officers early in his career for assaulting a black man on the street. People to this day, are influenced by pac and his message. He had to go, same goes for Michael Jackson. When they tried to label him as a child molester phedofile, it was bullshit, most people dont believe it. Jackson was killed by the higher ups, same with Tupac. Just my opinion