That is all speculation really.  Nobody knows exactly what happen.  Pasolini had a
habit of continually speaking out about the Italian government.  It was no secret
that he was a homosexual and one theory is that the boy was sent as a patsy because
he was underage.  Apparently, he was jumped by another group and killed that
night.  This theory is covered in the excellent film WHO KILLED PASOLINI which was
made I believe in 1995 and produced by Mario and Vittorio Gechi Gori.  Director
escapes me at the moment but Morricone did the soundtrack (being no stranger to
scoring Pasolini's work).  The film is incredibly interesting and depicts theories
of a cover up, etc. It is very convincing and those interested should try and seek
it out.  I saw it locally at a local art house theater.

I am not sure if this is still available but a great book on Pasolini as available
from Princeton Books:  Pier Paolo Pasolini: Cinema as Heresy by Naomi Greene
(published in 1990. ISBN 0691000344).

One thing is for sure, this man was very complex and almost always misunderstood.

Mark