(Michael P. Tremoglie is a former Philadelphia police officer and the author of "A Sense of Duty," available at Barnesandnoble.com and Amazon.com.) ONCE AGAIN, another killing - this time a double murder - in the city. Once again, the murderer has at least one prior violent felony conviction. Mustafa Ali has allegedly confessed to killing two armored-car security guards while they were collecting money from an ATM in Northeast Philadelphia. He has a federal conviction for bank robbery. He served just six of the seven years he was sentenced to in 1993, followed by seven years of supervised release after...