Japanese by Example
Learning through examples in manga

I say that because I thought it up with だって

名探偵コナン » Volume 1 » Page 111

A fake kidnapping ploy turns into an actual kidnapping. After the kidnapped child is safe, her father goes after their butler for concocting the scheme. The daughter, Akiko, protects the butler, saying she’s the bad one.

晶子(あきこ):
「だってこの誘拐(ゆうかい)事件(じけん)(かんが)えたのは、晶子(あきこ)なんだもん!!」
"I say that because I'm the one who thought up the kidnapping plot!"