The phrase "after he observed" is correct and usable in written English.
It can be used to indicate that an action or event occurred following someone's observation of something.
Example: "After he observed the unusual behavior of the birds, he decided to investigate further."
Alternatives: "after he noticed" or "after he witnessed".
Conover says he even came to relish opportunities to use brute strength against inmates after he observed them disobeying orders and attacking officers.
But, he said, after he observed violations and deficiencies in crew training, crew fatigue and other problems, he tried to bring a case against the airline and was blocked by his F.A.A. managers.
Dr. Monnett confirmed for the investigators that after he observed the dead bears, he contacted Dr. Derocher and others about what to do about his observations, since they were polar bear experts and he was not.
"No other study had ever measured the effects of bats' insect consumption in a natural forest," said Dr. Kalka, who had been among the first to realize the importance of bats in controlling insects on plants, after he observed them with night vision cameras.
He discovered this new approach to painting after he observed that glossy paint left a film of color on the surface of the water as he washed his paintbrushes.
Eccleston accepted the role and helped Davies make the character more human after he observed that "Baxter was getting lost amid his loftier pronouncements".
But Goat Man gains the upper hand after he observes this hustler receiving oral sex from a man on the edge of Wendy's pool.
A glimpse into Mendleman's creative process is found in a two-page spread after he observes the bustling market crowd.
Soon after, as he observed the Paris student revolts and the protests against the Vietnam war, it became clear to him "that under the heading of systems are also social systems.
After all, he observed, "many more of Larkin's writings have passed into the national memory".
The only author to study the offspring of the chimeras after birth, he observed that 20% of the 121 mice developed tumors.
