A Rikers Detainee Made a Daring Escape. The Getaway Car? A City Bus.

Some jailbreaks require elaborate planning. Others demand feats of strength or agility. Few have relied on the New York City bus system.

But that system unwittingly supplied the getaway vehicle when a Rikers Island detainee made a break for it outside Bellevue Hospital Center on Wednesday night, two people with knowledge of the incident said.

The detainee, James Mossetty, had been jailed since January on assault and drug charges, and he was taken earlier this month to Bellevue, where he was treated for psychiatric problems, among other things, one of the people said.

On Wednesday night, just before 10 p.m., two New York City Department of Correction officers were supposed to be putting Mr. Mossetty into a van for a return trip to Rikers when he somehow escaped from the hospital’s secure loading area, the city officials said.

He climbed a median, dashed across several lanes of traffic on the nearby Franklin D. Roosevelt Drive and boarded a city bus to make good his escape, said the people with knowledge of the matter, who spoke on the condition of anonymity to discuss the security lapse.

As the authorities searched for him on Thursday, unanswered questions abounded. It was not clear, for instance, how Mr. Mossetty, a 35-year-old with a history of mental illness who was supposed to have been handcuffed, slipped away from the guards.