If by natural you mean you want them to seem like they are coming from a native English speaker. I found the teachers memo saying he is going to buy lottery tickets next week. Diplomacy is an important skill when dealing with conflict. The detectives concluded from the investigation that the culprit was none other than the manager himself. The journalist was so passionate he worked all through the night with no sign of stopping. The usage of English words change from time to time.

I found the teacher's memorandum, which states that he is going to buy lottery tickets next week. - (Add a comma before "which", assuming what follows is parenthetical) Diplomacy is an important skill to have when dealing with conflicts. - OK The detectives concluded from the investigation that the culprit was none other than the manager himself. - (Change "culprits" to singular.) The journalist was so ardent that he worked all night without a sign of tiredness. - OK The usage of English words changed from time to time. - OK