Canto 3 -
Araṇya-kāṇḍa
Chapter 43: Sītā Sees the Magical Deer
Text 3.43.38

एतेन हि नृशंसेन मारीचेनाकृतात्मना।
वने विचरता पूर्वं हिंसिता मुनिपुङ्गवाः॥

etena hi nṛśaṁsena mārīcenākṛtātmanā
vane vicaratā pūrvaṁ hiṁsitā muni-puṅgavāḥ

etena = this; hi = for; nṛśaṁsena = cruel; mārīcena = Mārīca; akṛta-ātmanā = and evil-minded; vane = in the forest; vicaratā = while he wandered; pūrvam = formerly; hiṁsitāḥ = has injured; muni-puṅgavāḥ = great sages.

For this cruel and evil-minded Mārīca has formerly injured great sages while he wandered in the forest.

Lord Śrī Rāmacandra now reveals Mārīca’s evil nature as the reason for him to be killed [by Rāma].

Mārīca was cruel because he was a murderer.