The phrase "had surmised that" is correct and usable in written English.
It is used to indicate that something has been concluded after considering the available evidence. For example, "After examining the clues, Sherlock Holmes had surmised that the murderer was the butler."
Diplomats and analysts had surmised that the Kremlin might draw the process out as part of negotiations with the West.
I had surmised that perhaps McGregor's biggest opponent could be himself or rather more accurately the trappings that being a modern day UFC star can bring.
In grand jury testimony read during the trial, Mr. Inclán agreed with a judge who had surmised that Mr. Inclán had taken a "don't ask, don't tell" policy with campaign cash.
The Church approved the rescuing of Oscarey; and it was anticipated, as Mr. Flewett had surmised, that when old Canon Furney died the benefice of Clonbyre, Nead, and Oscarey would become one again, and that the unnecessarily spacious, drafty rectory in poor repair at Clonbyre would be abandoned in favor of a smaller, more comfortable one at Oscarey.
Unaware of the now deep if not quite universal worship of the Federer game, she had surmised that the fans started out pulling for Monfils — rooting for the underdog, as they do in most instances — but that, because Federer was now trailing, they were feeling sorry for him and giving him encouragement.
After reviewing the surveillance footage, he and his investigators had surmised that the murders had taken place sometime between nine A.M. and three P.M. on Friday, but now, said Ríos, that window had been reduced to three hours, from noon on.
This does not mean, as some have surmised, that Grubman put the car in reverse, thinking that it was in drive.
Maybe the GOP doesn't remember the episode with sufficient clarity or perhaps they've surmised that, as was the case with Obama, it's politically survivable.
Some researchers have surmised that, as with DENV, when antibody-virus complexes attach to Fc-receptors, viruses are brought close to cell surfaces, where they enter the cells by normal mechanisms (31, 32).
Who but a genius could possibly have surmised that "Made In Scotland.
Gore was typically guarded, but one might have surmised that he was rethinking some of the traditional Democratic positions.
