Both.
You could handle Read a Sitch and Read a Person differently, sure. There is precedent, (while you ran out on that balcony over looking the fight, you manage a few observations... what are they?) in these cases it makes less sense that they also saw something else in retrospect later because of that earlier vantage... but then again, why not? I personally let the read a sitch carry, in just the same way that I would allow them to ask the same question multiple times and give them different but correct answers each time, or refund their question. What is the biggest threat? The guy with the mini gun and that lopsided spaced out smile. What is the biggest threat? The next big issue is probably... (fill in)
In your situation, they arrived to find a grizzly murder scene. I personally wouldn't allow read a sitch, I'll cover why later, but to begin with, say you do. They think it might be dangerous and look around. What is the true location of my enemies? no one here seemly overly hostile to you (or maybe some bystanders ARE?), but there is a blood trail leading west... (+1 forward to find them). What should I be on the look for? Motive. In fact, you recognize... In fact, one of the bodies has three times as many bullet holes... In fact, the bloody footprints through the area seem to all collect around that corpse... (+1 forward to interact with that observation). Ask it again maybe?
If there are no answers for any of the questions listed, the situation isn't actually charged. Just the same, if the +1 forward to act on the information in this scene isnt relevant, the sitch isn't charged. Keep that in mind, +1 forward means rolls happening right Now, what are the other base moves, is this a sitch where those could matter yet? If there is no danger here, just because the players believe there might be, doesn't automatically charge the situation. Although, you can always leave Threats in the area, and if they do read a sitch, maybe instead of nothing happening, maybe they find an opportunity via seeing a threat before it reveals itself and thus get additional info/intel/whatever. If the situation is not charged, they're welcome to investigate asking any questions they wish, and you can give them all the observations you want. The longer they stay, the more they find out. Maybe they can even take the corpses to the near doc for better questions.
In your situation I would've told them the sitch is not charged, a quick look around will reveal a dearth of enemies. Let them investigate themselves. I would also theme whatever they ask in answers that fit their concept. Not a tracker? No track mentions. Not a Doctor? limited forensic information. Not a savvyhead? limited tech observations. Etc. Each playbook (and player concept) has a focus that will bring new and interesting stuff to light. Flavor. If they wanted to know where the fuckers went, I'd give clues if that was reasonable, or let someone open their brain to the scene for those extra sweet goodies the maelstrom is just WAITING to tell them. Like where they mightve run off too...
Read a Sitch and Read a Person are snap observations that are intuitively connected with PEOPLE and BEHAVIOR. Read a Sitch is not Spot/Search from D&D, even if it functions like that when spotting enemies, threats, or otherwise. They do not naturally give extra details about corpses, tracking, scenery, etc unless those are Threats right now. Like maybe the bodies are in a landscape threat, like the badlands where ten raider groups war over whatever... now how long do you got before They get here? sitch might start.... START getting charged. Open your Brain is exactly what should be used in your example, assuming you don't want to connect the scenes in an immediate there he went! (chase scene) as shown in my first post.
The reason I find the ASK ANYTHING on a 10+ with hold 1 too powerful, is first of all it can be used to ask anything. So if you're talking to another player and you and they are a bit on edge and potentially violent, you've got the ability to force their player to tell you any one thing: Where is the thing you're hiding from me? Where is the person you love most? What horrible thing have you done in secret? <== Those questions might be appropriate powerful weapons for the character that has already advanced (unlocked/earned) his moves AND rolled damned perfect (rare), but a 10+ is easy street into shit that they haven't earned the right to know yet. (they could ask In Character, they could earn it that way, they could go find out via npcs or whatever risking tip offs, but they don't get to just pull it out of the air just cause they hit a (easy to hit roll). Its too much, too early, and makes the advance less AWESOME. All bad in my opinion, but functional sure.
Read a Sitch hitting advance on a 10+ is also bad In my opinion. Because you shouldn't be able to ask ANYTHING and then get that lovely +1 forward through it all just cause you rolled a 10+ There will almost never be an instance where that isn't better then the three questions. Additionally, It might be used like spot. OH Shit bodies!! charged? 10+ who killed them? Answer. Erm... No, this doesn't sit right with me. It should be.. OH Shit bodies! Go find out who did it, go look and ask, you dont need read a sitch to ask the mc questions about a thing. Also, +1 forward while acting on the information can give someone who asked the right question, a +1 forward for every single roll until the scene is over. That's not a 10+ range, thats a 13+ (in my game) and an advance later.
Your biggest issue was that you didnt actually have a charged sitch, but you didn't want to tell the players that until they found out for themselves. Thats on you. In this case, the fact that they made the move at all was extraneous and so of course the hold felt useless. A charged sitch means there ARE enemies/threats, Right Now. The false perception of danger is enough to get people anxious, but not enough charge the sitch. What would you do on a miss? Create danger that wasn't there? If that even crossed your mind, then you should've just created danger there to begin with. Bodies are just a thing in the wasteland. No matter who they are, or how much they've been ripped apart. Its Scenery now. The exception is when the danger hasnt passed, (really) the guy is gasping his last voiceless deathknell, blood freshly pooling, something clatters down the alleyway in full sprint... (and intends to do more harm).
I may have repeated things, I'm sorry if so. This is all stream of thought and edited for the glaring Spelling errors. AW works in a variety of ways and it the pace is different for each group. What works with one might not work with another, but I've found if a move doesn't fit right, you're probably not triggering it. I've had many investigations happen in my game, and I used to use Read a Sitch too... but I found that was just a lingering bad habit. If you need detective moves, make one. Though keep in mind, that the act of making the detective move... removes the actual detective work completely, it means the player cannot ask freely, they can only ask what their rolls allow.
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Detect: When you're looking at the evidence of a mystery and you've finished asking the MC questions about what you're seeing, roll+sharp. On a 7-9 you find a clue. On a 10+ you find three clues. Tell the MC where the clue was, pick one: On the Victim, In the Scene, Coming or Going, Something left behind or missing, or About the Perp; and the MC will tell you about the clue. On a miss, the MC can make a hard move, as hard as he likes.