"Cry Freedom" is available at Amazon.com --
here.
You will also find, through searching the archives, the testimony regarding his murder at the Truth and Reconciliation Commission. His family petitioned the Constitutional Court (along with that of Griffiths and Victoria Mxenge's) because they did not want the murderers to be granted amnesty. Their action failed, but that did not necessarily guarantee them amnesty. The result of the amnesty hearing is on the TRC site.
The hearings took place in Port Elizabeth between the 8th and 11th of April 1997. Find links to the testimony
here.
I most certainly stand to be corrected, but as far as I recall, Biko was never associated with the PAC, certainly, their sketchy website never mentioned him in the organisation's origins. In fact, he is usually termed a "Black Consciousness" leader. He was deeply involved in Student Unions and was a leader of the BPC - the Black People's Convention.
Here is a brief biography.