Don't be silly. If a murderer burns the clothes in which he perpetrated the murder, he's not 'destroying evidence' in addition to being a murderer. Something must first have been determined to be evidence, before destroying becomes a criminal act. Neither are you obstructing justice by hiding evidence.
Actually, I believe that is the case, although the charge pales in comparison to murder. IANAL, but the Green River Killer was convicted of contaminating a crime scene because he left false evidence to throw off investigators. From that, it appears that intentionally tampering with evidence of a crime - even if you created it - is illegal.
