That is a very easy one.
Arnold Beverly has CONFESSED to doing so.
The courts have refused to hear this evidence, DESPITE:
1. a confession by Beverly that he killed officer Faulkner, and that Mumia did not do so.
2. The clearly unconstitutional exclusion of many African-Americans from the jury pool from the jury.
3. A "hanging" judge who had it in for Mumia.
4. A trial filled with errors and with political attacks on Mumia for his Black Panther Party activities and revolutionary opinions.
You can actually watch the video of the confession on-line. These facts are well known to the courts involved, and to the mainstream media, which have been suppressing the truth. There also are some newly discovered photographs from the date Mumia was arrested.
Here is the link for the video:
www.labournet.net/mumia/0705/confess1.html

FREE MUMIA NOW!
DOWN WITH THE U.S.'s RACIST JUSTICE SYSTEM!
FREE ALL POLITICAL PRISONERS HELD IN U.S. PRISONS AND JAIL, HERE AND AROUND THE WORLD! FREE ALL U.S. PRISONERS!
DOWN WITH U.S. IMPERIALISM!