The most common and most likely answer to this crossword clue is the 10 letter word INDICATION
I've seen this crossword clue in The Times
I
N
D
I
C
A
T
I
O
N
Buddy explains!

The straight part
We know that "piece of evidence" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case piece of evidence = indication.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 INDICATION mean?
INDICATION noun- Act of pointing out or indicating.
- That which serves to indicate or point out; mark; token; sign; symptom; evidence.
- Discovery made; information.
- Explanation; display.
- Any symptom or occurrence in a disease, which serves to direct to suitable remedies.
- An declared approximation of the price at which a traded security is likely to commence trading.