。
She wanted to punish only those responsible.
Literal
She [topic-は] responsible people [only-だけ] [object-を] punish-want [quotative-と] was-thinking.
責任ある人々 uses ある directly after 責任 in an attributive position — 'people who have responsibility.' ~たいと思っていた layers desire (~たい, 'want to') inside a thought (~と思う, 'think') in the past progressive (~ていた). This captures her ongoing past mindset: 'she was thinking she wanted to punish only the responsible ones.' 罰する (ばっする) means 'to punish.'