Learn Spanish (Latin America): El que cometió el plagio fue el competidor. - The one who committed the plagiarism was the competitor.

This is a pseudo-cleft sentence, which is a structure used to emphasize a specific piece of information. By starting with El que (The one who) and linking it with fue (was), the speaker shines a spotlight directly on el competidor. It strongly contrasts the competitor with anyone else who might have been suspected of the plagiarism.

Could I use quien instead of el que in this sentence?

Yes! Because the subject is a person, you could absolutely say Quien cometió el plagio fue el competidor. Using el que is very common in everyday spoken Latin American Spanish, while quien can sound slightly more formal or written, though both are perfectly natural and correct here.

Why is the linking verb ser in the preterite (fue) rather than the imperfect (era)?

In these emphasized pseudo-cleft structures, the linking verb (ser) usually matches the tense of the main action verb. Since the plagiarism was committed as a single, completed action in the past (cometió, which is in the preterite), we use the preterite fue to maintain tense harmony in the sentence.

Does Spanish use cometer the exact same way English uses "to commit"?