Why was Gerry Pappa killed?

Wikipedia says it was in revenge for killing Ralph Spero who was a suspected Stool pigeon.
This would be the same Ralph Spero that had a bust up with Sammy Gravano which caused him to be transfered to the Gambino's.

Was Ralph Spero made?
Did Pappa simply decide to kill him off his own initiative?
Why did the Chin allow him to be killed? - was he pissed off with Pappa's violent ways?
Finally, was Pap the guy who actually started the windows racket or was he simply the appointed Genovese representative?

Cheers