The most common and most likely answer to this crossword clue is the 8 letter word INQUESTS
I've seen this crossword clue in The Times
I
N
Q
U
E
S
T
S
Buddy explains!

The straight part
We know that "Investigations" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case investigations = inquests.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INQUESTS mean?
INQUESTS noun- A formal investigation, often held before a jury, especially one into the cause of a death
- An inquiry, typically into an undesired outcome
- The jury hearing such an inquiry, and the result of the inquiry
- Enquiry; quest; search