Looking on the internet deeply has found these results:

in a school shooting is the most popular phrase on the web.

at a school shooting 1804,000 results on the web	in a school shooting 11,530,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I mean, it's not terrorism or a school shooting. GEMMA: It's about that school shooting yesterday. After the school shooting, we fingerprinted all the students. School shootings fit the classic copycat model. Don't worry, it's just another school shooting. You know, Charlie's math proves that our main suspect does fit the shooter profile for a school shooting. In Erfurt in Eastern Germany 17 people were slain in a school shooting five years ago. Everybody be cool, this isn't a school shooting!	Everybody be cool, this isn't a school shooting! In Erfurt in Eastern Germany 17 people were slain in a school shooting five years ago. GEMMA: It's about that school shooting yesterday. I mean, it's not terrorism or a school shooting. After the school shooting, we fingerprinted all the students. You know, Charlie's math proves that our main suspect does fit the shooter profile for a school shooting. School shootings fit the classic copycat model. Don't worry, it's just another school shooting.

at a school shooting

1804,000 results on the web

in a school shooting

11,530,000 results on the web

More popular!

I mean, it's not terrorism or a school shooting.
GEMMA: It's about that school shooting yesterday.
After the school shooting, we fingerprinted all the students.
School shootings fit the classic copycat model.
Don't worry, it's just another school shooting.
You know, Charlie's math proves that our main suspect does fit the shooter profile for a school shooting.
In Erfurt in Eastern Germany 17 people were slain in a school shooting five years ago.
Everybody be cool, this isn't a school shooting!

Everybody be cool, this isn't a school shooting!
In Erfurt in Eastern Germany 17 people were slain in a school shooting five years ago.
GEMMA: It's about that school shooting yesterday.
I mean, it's not terrorism or a school shooting.
After the school shooting, we fingerprinted all the students.
You know, Charlie's math proves that our main suspect does fit the shooter profile for a school shooting.
School shootings fit the classic copycat model.
Don't worry, it's just another school shooting.