Make a very good list of everything that was destroyed, along with its age, original purchase price and, to the extent possible, reasonable replacement value. (Sorry, even if whatever was damaged "looked just like new", they're going to depreciate its value.) Also make a list of your additional costs - the bill if you had to spend the night in a hotel, the bill, the cost of a carpet cleaner, etc. You can try making a claim for your missed time from work, but I doubt they'll offer to compensate you for that.

Then ask your landlord to forward it to its insurance company. See if they make you an offer. They may suggest that you bear full or partial responsibility for leaving your window open with your apartment unattended. They may say "We don't cover this type of claim." But you won't know until you try.

I'm assuming you didn't carry renter's insurance. Now you're probably getting a sense for why it can be a good idea.