The burden of proof for conspiracy charges is very low. They do not have to prove anyone actualy did something illegal, just that they thought about, talked about, or planned to do it.
No they do not have to prove anyone did anything illegal except:
1. Agree to commit a crime, and
2. Commit an overt act (not an illegal act but one that is in futherance of the conspiracy, in arson it may be buying a can of gasoline)
I don't think that if #1 and #2 are accomplished you really want the police to wait until they set fire to something.
In this case,
1. Someone was threatened (the girl).
2. NYPD found a loaded weapon in his vehicle, a crime (just as they did David Berkowitz, I suppose they should have let him go too).
3. The guy has a felony "GUILTY PLEA" that means he admitted he did it, no appeal rights.
4. A "subsequent search" of his apartment doesn't say with or without a warrant or consent. That will come up in his trial. I can think of several ways to justify a warrantless search.
He was a US Army veteran. Doesn't say if he was a Ranger, cook, finance clerk or whatever. There are many veterans who are criminals. I can't see why being a veteran (I'm one) should give you any breaks in the criminal justice system. Physcological tests for things like Special Forces concentrate a lot on ability to think independently and not likely to abuse your position just like police tests do. The article quotes he had poor stress tolerance, judgement, impulse control, and immaturity. Any one of those things would prevent you from being selected for Special Forces or the police department and they should.
I say good job NYPD!
Many here have made him some kind of martyr. This is exactly what anti-gun people can use for ammunition in arguing for more gun laws.