* Based on the scattered clues, I surmise that the thief entered through the back window. (meaning: to guess or infer)
* From her worried expression, I surmised that she had received some bad news. (meaning: to deduce or conclude)
* The detective surmised that the victim knew the perpetrator, but he had no concrete evidence to support this claim. (meaning: to form an opinion without sufficient evidence)
Let me know if you'd like some more examples!