What Paul means by "I was alive once without the law" is that, at one time, he without the knowledge of what the law meant. It was "when the commandment came" that he understood. At this point, Paul knew that he was as good as dead because he had broken the law (Romans 6:23).
Notice that it was not the law that killed him but sin! Plain, simple truth—sin slew him. By contrast, Paul says that the law was ordained to life. It is holy, just, good, and spiritual. That is very clear.