The most common and most likely answer to this crossword clue is the 10 letter word EYEWITNESS
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result EYEWITNESS
- Heard I could be wisest to hide name of person at the scene
- Regard card head shows trial participant
- Person at the scene perhaps sees win yet is upset
- Person observing tree with it, in strange sense
- Seer who may be called to account?
- Mention of the first person with ingenuity on headland as observer
- Observer, I heard, distorted its news
- He saw you earlier, coming back, taking boiled sweets in
- One who watched the start of ‘The Sweeney’ is upset
- Spectator beginning to engage you with news — it’s awful!
Buddy explains!

The straight part
We know that "Seer who may be called to account" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case seer who may be called to account = eyewitness.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 EYEWITNESS mean?
EYEWITNESS noun- Someone who sees an event and can report or testify about it.
- To be present at an event, and see it