''I was concerned that it wasn't going to be good enough to pass for the original,'' he explained in court, ''so I told him I needed to see it.'' Mr. Hochhauser said he later determined ''it was good enough.''

There was one other big problem. The Dalí's position at the entrance to the jail was in plain view of two guard stations that are staffed at all times. Mr. Nuzzo, whom Mr. Hochhauser said was the master planner, and he would need two accomplices and a ruse to get everyone else out of the area for at least a few minutes.

In addition to Mr. Pina, they recruited Mr. Sokol, a 14-year correction officer, as a lookout, Mr. Hochhauser said. The plan was set, he said. Sometime around 1 a.m., Mr. Hochhauser would start a false fire alarm, during which all jail staff members are trained to meet at a staging area nearly a mile from the jail's entrance to put on fire retardant equipment and head toward the emergency.

Only Mr. Nuzzo, he said, would hang back near the entrance, while Mr. Sokol and Mr. Pina unlocked the case, removed the Dalí and stapled the fake in place. Mr. Nuzzo, he added, would hustle the original to his car and place it in a storage facility he would rent over the Internet under a fake name. ''It was a great idea for us to cover this up,'' Mr. Hochhauser said he and Mr. Nuzzo concluded.

After an aborted attempt in the wee hours of Feb. 28 -- ''too much staff traffic,'' Mr. Hochhauser told the prosecutor -- they tried again a day later, and pulled off what they thought was a flawless caper, give or take a few glitches. One glitch, according to court documents and interviews with Rikers staff members, was one Officer Pearson.

Officer Pearson manned the arsenal, one of the two posts at the jail's entrance. According to prosecutors and jail officials, when the fire alarms sounded, Officer Pearson refused to budge. But Mr. Nuzzo, they said, ordered him to take his lunch break, and Mr. Sokol and Mr. Pina then removed the painting and placed it in Mr. Nuzzo's S.U.V.

Later, ''He handed me the car keys,'' Mr. Hochhauser said on Monday, ''which told me that the mission was accomplished.''