Entirely different methods of operation. Yes, a professional hitman would spend a month just learning the judge's travel patterns. Then he'd probably just tie a grenade to his car and walk away. Another hitman would find a suitable position along the way and would make his attempt as the car stops at a red light, or when he parks at home. But if you look around most suburban residential areas, there aren't any highrises to use, and it's all hidden among trees. It's still possible to do, but it requires experience in such kind of stalking. Many, like myself, read about it and saw a few movies, but hardly anyone actually have done it.
An attack at his office is different. All that the killer needs to do is to get inside and to carry a suitable weapon with him. Getting inside a public building is not too complicated; getting a weapon carried in is also possible in many different ways. Those are separate, independent phases that have nothing to do with each other, and they can take as long as they take. The victim will be still at his office, every single day; and the killer is not risking anything as he is approaching the office, entering, and even as he is leaving - there is nothing to suspect him with. It's likely that the killer knew where security was after hours, and where it wasn't. Besides, who'd stop a plumber or a telephone repair man after hours? That's the best time for them to do their work.
One would think that a similar attack could be carried at judge's home. But that's possible only if one assumes that the doors at his home are easy to open, and that nobody else is present at his house. Both assumptions are probably false. If there are several family members inside, it's difficult to ensure that none of them calls 911 or presses a hidden alarm button (every house alarm setup has one.) A large team, with good preparation, could do it, but teams come with their own vulnerabilities. This was done by one operator.
Based on some quantity of crime fiction that I have read, the murder of the judge was done quite professionally. Nobody saw anything, and they don't have a suspect. If they check the video records they may find that someone wearing a disguise was entering and leaving the office. That disguise is gone, and the killer is out of town already (was gone, probably, before the body was found.) There is nothing to connect the killer and the judge, besides someone who had a problem and who paid some Bitcoins to someone unknown for having this problem removed.
You've never been to that courthouse have you. Only a few people are allowed to bypass security going into the tower that contains the courtrooms and judges chambers, and they all have to get their passes renewed each year. About the only people allowed to carry guns in that part of the building are judges and bailiffs.
I'm sure Sheriff Kaelin personally investigated Judge Greenwell's chambers. If his office said Judge Greenwell committed suicide, I would believe it.
Indeed. Seems it was the Judge himself. Which, of course, raises the question of motive ...
But you raise an interesting theoretical question about modes of operation.
There is outside mode, as in Lee Harvey Oswald taking a shot at Major General Edwin Walker on April 10, 1963, as he sat at his desk preparing his taxes. Bullet deflected by window frame. Walker lives. Oswald escapes. Cops are laughably clueless until Kennedy dies, and investigators learn the truth from Oswald's Russian wife and writings he left behind.
Then there is inside mode. I don't have an example off the top of my head. But it requires careful preparation and thought to pull off without getting caught. There are cameras. There are a limited number of people who could have done it. Etc. You may know where security usually is at a given time. But how about when you actually pull the trigger?
There is also in-between mode. Where the killer is a former insider, not trusted sufficiently to breeze past security. Dan White comes to mind. Former SF cop, fireman, and city supervisor. Had differences with the mayor and another supervisor.
Security? Bah! White climbed through a window carrying a .38. Confronted the mayor. Bang! Then off to the supervisor's office. Bang!
Diminished capacity due to depression and consumption of excess Hostess Twinkies. Got only seven years. Served five. Committed suicide via carbon monoxide.
Of course, when it comes to bypassing building security, perhaps the best example is probably Harvey's Resort, a casino hotel in Stateline, Nevada. Half a ton of dynamite inside a large "IBM office copier" wheeled into place by "workmen". Then came the extortion demands ($3m in 24 hours — this was 1980).