Given that the match penalty Douglas Murray received after his check to the head of Mike Kostka carried with it an automatic indefinite suspension, it's really no surprise that the NHL has chosen to suspend the veteran blueliner 3 games.
I don't think Murray wanted to hit Kostka dirty, but this hit is the result of the way Murray plays, bad hockey sense, and his limited skill set.
Kostka doesn't alter his angle of attack, Murray just reads it poorly and misses him, and when he realizes that he missed the check, he chicken wings out his elbow and nails Kostka right in the head, causing a clear concussion.
Murray has a clean suspension record, and doesn't have a reputation as a dirty player, though his rapid aging has put him in more and more situations where his hits are borderline.
Jarred Tinordi will draw into the lineup in Murray's absence, and we can all hope that he asserts himself well enough to keep Murray out of the lineup when his suspension is over, and into the playoffs. It is unclear as of yet whether the Canadiens will call up a defenseman during Murray's absence to ensure they have an extra body, but if they do, expect it to be Nathan Beaulieu.