JINDO, South Korea — South Korean President Park Geun-hye said Monday that the captain and some crew members of the sunken ferry committed “unforgivable, murderous acts” in the disaster, which left more than 300 people dead or missing.

The captain initially told passengers to stay in their rooms and waited more than half an hour to issue an evacuation order as the ferry Sewol sank Wednesday. By then the ship had tilted so much that many of the roughly 240 people missing are believed to be trapped inside.

At a Cabinet briefing, Park said the captain and crew “told the passengers to stay put but they themselves became the first to escape, after deserting the passengers.”

“Legally and ethically,” she said, “this is an unimaginable act.”

The captain and two crew members have been arrested on suspicion of negligence and abandoning people in need, and prosecutors said Monday that another four crew members have been detained. Senior prosecutor Ahn Sang-don said prosecutors would decide within 48 hours whether ask a court for arrest warrants for the four — two first mates, a second mate and a chief engineer.

Video showed that captain Lee Joon-seok, 68, was among the first people rescued. Some of his crew said he had been hurt, but a doctor who treated him said he had no fracture and only light injuries.

Lee spoke of “pain in the left rib and in the back, but that was it,” Jang Ki-joon, director of the orthopedic department of Jindo Hankook University. Jang said he did not realize Lee was the captain until after he treated him.

So far 64 bodies have been recovered, and about 240 people remain missing.