How would D&D 5e spellcasters investigate an anonymous attack?

Question

The adventuring party (D&D 5e level 5) have just managed to commit an audacious attack, destroying an important, visible monument. For the sake of argument let's assume that they have managed to do so without anyone seeing who the attackers were and how they did it, and did not leave behind any "nonmagic" evidence leading to their identities, but did not take any magic precautions.

Immediately after the event the attacked organization is angry, and has significant resources (though player-level appropriate, not wishes or artifacts) and multiple casters (divine and arcane) on site.

What spells and/or magic items would they use to try to find out what happened and who it was?

I looked over the divination spells, and I was surprised that I did not find anything that seemed immediately useful; for example, 4-th level Divination is limited to things that will happen in 1-7 days, but not about what happened ten minutes ago; and there are various spells that would help find a stolen object, but in this case the action was purely destructive (but non-lethal), the party did not take anything. I would expect that in the relatively high-magic D&D setting there must be some magic resources that a powerful organization would use, but what are they?

Answer 1

There are a number of spells that help with investigations such as clairvoyance, enhance ability, or scrying. However, with no physical evidence whatsoever, the only good option you have is to ask a witness.

While you said "without anyone seeing", there are other possible witnesses. Finding such a witness could involve this same investigation, followed by a spell like locate creature.

Speak with Plants or Animals

Some such witnesses include plants nearby or critters who may have nested in and around the monument. Speak with plants says:

You can question plants about events in the spell’s area within the past day, gaining information about creatures that have passed, weather, and other circumstances.

And speak with animals says:

at minimum, beasts can give you information about nearby locations and monsters, including whatever they can perceive or have perceived within the past day.

Ask a God or Other Entity

If no mortal witness is present, you could seek the beyond.

The spell commune asks a deity (which is especially thematic if the monument was religious in nature):

You contact your deity or a divine proxy and ask up to three questions that can be answered with a yes or no.

...and contact other plane can query other extraplanar entities:

On a successful save, you can ask the entity up to five questions.

Follow the lead

After getting a lead, those original investigation spells or locate creature (along with other locate spells) can be used to follow up on that lead.

Once the organization has enough information to pull in some suspects, spells like zone of truth, detect thoughts, or dominate person can compel the truth.