Your neighbour is suspected of brutally murdering their parents in his backyard. One Sunday afternoon, you maw their lawn along with yours because they're really old and it really isn't that much work once you're at it anyway.

In the process, you destroy the evidence exonerating them, i. e. footprints of shoes much smaller than theirs.

Obstruction of justice? Nope.

Now imagine the same thing happened. Except that this time, you include their lawn not just because you always do, but to get them thrown in jail. You're really tired of doing all these chores for them, and it's time for new neighbours.

Obstruction of justice? Yep.

Intend matters.