Here's a list of examples I've seen:
- What do you think happened?
- Who do you think has killed him?
- Who do you think he killed?
How does this structure what/who do you think... work? It seems a bit odd that you've got happened after think in the first example, has killed after think in the second. In third, who and what have got nothing to do with the first clause in the sentence but with the second. Can it be used in the past and in the future? "Who did you think (had) killed him? Who do you think will call him?"
Apparently it can appear in the middle of any question when someone asks an opinion. Is that so? Are there more structures like this?
What happened?
Who has killed him?
The third is the odd one out. Remove the 'do you think' and it makes no sense:
Who (has) he killed?
I am no grammarian as many here are, but I would suggest we need to try and understand why the sub-clause 'do you think' eliminates the need for the perfect tense and allows the simple past in the third example. It would, of course, take the perfect 'Who, do you think, he has killed? I'm afraid this is a job for an Ashworth or a Fine.
– WS2 Nov 12 '13 at 10:48