"Wir prüfen, was passiert ist."
"We are checking to see what happened". While I realize sehen was not part of the original sentence, in English "We are checking what happened" sounds weird. I never know when to translate most literally or not. Would other translators out there mark my answer as correct?
I wouldn't because it's too wordy. It means effectively the same, and checking sounds weird to me. But "prüfen" is examine or test as well as check, which is clear in English.