OMG. Not a crime to destroy evidence to federal witness tampering? Unless the authorities
asked for it first??

What planet are you on?
Oh, the gun that man was shot with was my personal property. So I chose to melt it down, officer. You ain't got nothin' on me now -- no law against that, right?
Yeah, um; doesn't work that way. Obstruction of justice. Tampering with physical evidence. And in this case, preceded by aiding and abetting federal witness intimidation. How many crimes is that in itself? A few subpoenaed phone records, and the proof of intent is well enough established to raise the possibility of charges of Obstruction of Justice (Witness Tampering)...
...By intimidation (18 U.S.C. 1512(b))
...By destruction of evidence (18 U.S.C. 1512(c))
...By harassment (18 U.S.C. 1512(d))
These are all separate Federal crimes, i.e. all separate charges, separate punishments.
Here's a listing of the Federal statutes, with explanations. And here's NY's version of the
relevant felony statute for evidence tampering, for one -- I suspect it's either verbatim or nearly so for CO, as it's boilerplate stuff throughout the land. Note that the evidence need not have yet been produced... Prospective evidence is entirely within its scope, prior to any official investigation or proceeding.
Not into playing legal expert at all, but
come on, this is just common knowledge: You don't get to destroy potential evidence to a crime just because it suits you. God, I would have hoped that was common knowledge, anyway..