OBSTRUCTION OF PROSECUTOR

Obstruction is not really about justice, in most cases.
In fact, the victim of obstruction is normally not the so called suspect at all:

Generally, obstruction charges are laid when it is discovered that a person questioned in an investigation, other than a suspect, has lied to the investigating officers. Wikipedia

Why is this? Because the abstract concept of justice has little or no connection to most obstruction cases. You know this because, by definition, the person being questioned is not a suspect.
So, what are obstruction cases mostly about?
They are about someone committing perjury, usually about a factual matter, ironically, which has little or nothing to do with the larger course of justice.
Take the Clinton impeachment, and the charge. Classic example. 
Whether Clinton had an affair with Lewinsky is frankly neither here nor there, regarding the larger course of justice, or regarding Clinton's fitness for his role as President, for that matter.

Similar claims were made against Hillary Clinton.
Martha Stewart went to prison for similar largely irrelevant misstatements.

• Former Vice-Presidential adviser I. Lewis "Scooter" Libby was convicted of obstruction of justice in March 2007 for his role in the investigation of a leak to reporters by Richard Armitage of the identity of a CIA agent, Valerie Plame. His prison sentence was commuted by President George W. Bush in July 2007, so that Libby was no longer required to serve a two-and-a-half-year prison sentence, but was still required to pay a $250,000 fine, be recorded as a convicted felon, obey probation terms, and be disbarred. Donald Trump pardoned Libby on April 13, 2018.

There is also anticipatory obstruction now, an even bigger kettle of bad legal worms:

"Anticipatory obstruction of justice" has recently appeared on the horizon in cases such as US v. Wolff.^[6] However, the operative section, 1519, passed in 2002, has thus far languished in quasi-obscurity. Titled “Destruction, Alteration or Falsification of Records in Federal Investigations and Bankruptcy,” the provision was passed under Section 802 of the Sarbanes-Oxley Act of 2002.

The text of the statute is relatively straightforward:

Whoever knowingly alters, destroys, mutilates, conceals, covers up, falsified, or makes a false entry in any record, document, or tangible object with the intent to impede, obstruct, or influence the investigation or proper administration of any matter within the jurisdiction of any department or agency of the United States or any case filed under Title 11, or in relation to or contemplation of any such matter or case, shall be fined under this title, imprisoned not more than 20 years, or both.