At the end it shows through flashbacks how the killer was evidently the killer right?
No it doesn't.
And there are two killers actually.
They tell the girl their "master plan", but there is no flashback.
Is it actually possible to figure out the killer through clues in the movie?
There are really only a couple of hints. At one point in the film, one of the side-characters asks one of the killers "Hey, didn't you used to date Drew Barrymore?" after she is killed, but it's brushed aside nonchalantly. Still, on a rewatch, it's noticable that they had history.
There is also another scene where all of the students (Killers included) are sitting around talking, someone jokes that one of the characters is the killer (And he is) and the dude is like "Naw, I didn't kill anyone" and immediately the OTHER killer cuts his eye at him and says "Nobody said you did". That's actually one of my favorite parts in the movie. Dude hit him with a fierce
"nicca if you don't shut the fukk up" look....
Lastly, the biggest clue is when Neve Cambell is being chased by one of the killers, she runs outside and runs into the other killer (Who wasn't in the gear). She thinks it's sketchy, but from an audience standpoint it feels more like a false flag...at that point in the movie you didn't know that there were two of them working together so when he later says "the cops said I scared him off" you kinda believe him.
For the most part, one of the killers (Billy) is kinda obvious. Stu was more surprising.
In case you haven't noticed, I was kinda a Scream fanatic growing up.