In cases of first-degree robbery based on bomb threats, New Jersey judges have insisted there be some physical manifestation to back up the words.

Prosecutors appealing two overturned convictions want that to change.

In State v. Williams and State v. Dekowski, they asked the New Jersey Supreme Court on Tuesday to adopt A rule requiring only that the robber’s conduct create an objectively reasonable belief that he is armed with a bomb.

Kelvin Williams allegedly walked into a bank on Oct. 8, 2008, wearing a hooded sweatshirt partially concealing his face, told a teller he had a bomb and demanded $7 million. The teller handed over $552. Williams was arrested a short time later at a nearby shopping mall.

A Camden County jury convicted him of first-degree robbery and he was sentenced to 14 years in prison.

Prosecutors say Christopher Dekowski, wearing a long-sleeved shirt, a baseball hat and sunglasses, walked into a bank on Sept. 27, 2007, told the teller he had a bomb and demanded money. He fled with $500.

A Union County jury convicted Dekowski of first-degree robbery and he was sentenced to 13 years in prison.

Separate Appellate Division panels found prosecutors had failed to prove the elements needed to sustain convictions for first-degree robbery.

The appeals panels cited case law that requires something more than just a statement from a defendant saying he or she has a bomb. There must be “conduct indicative” that the defendant might actually be armed with one, the court said in reversing Williams’ conviction.

That conduct could include gestures such as patting a part of one’s body or reaching inside clothing, the court said.

At Tuesday’s arguments, Justice Barry Albin asked if a threat has to be accompanied by some sort of display.

“Absolutely not,” said Assistant Camden County Prosecutor Jason Magid. “It’s an objectively reasonable belief” that the person does have a bomb.

“No simulation is necessary?” Albin asked.

“Actual simulation is not necessary,” Magid said. “It’s the overall impression.”

Deputy Attorney General Kenneth Burden said the very nature of bombs means a display should not be required. A suspect, he said, could indicate that the bomb is hidden and that it could be triggered by a cellphone or a timer.

Williams’ attorney, Assistant Deputy Public Defender Michael Jones, said the state wants the proofs for a first-degree conviction to be too loose.

“They want to hang you for a sheep when all you brought was a lamb,” he said.

Albin asked whether it would be adequate if the suspect was wearing extremely baggy clothes.

“The statute requires the display of an object,” Jones said. “The Legislature wanted an object displayed.”

Assistant Union County Prosecutor Meghan Tomlinson agreed with Burden that a bomb doesn’t necessarily have to be carried on the person.

“The victim may need little more than the threat itself” to believe there is a bomb, she said.

“Disturbing, bizarre behavior is not enough,” said Justice Anne Patterson.

“Disturbing, bizarre behavior in conjunction with a clear threat to use a bomb is enough,” Tomlinson said.

Dekowski’s attorney, Assistant Deputy Public Defender Rochelle Watson, also argued that a threat alone to use a bomb is not enough to sustain a first-degree conviction.

“In the absence of an actual object, there must be some physical demonstration,” Watson said.

“You can’t just take a defendant at his word these days?” Albin asked.

Watson said there has to be more to make the victim believe there is, in fact, a bomb and the suspect might use it.

“The person’s going to want to walk away with the fruits of the robbery,” she said.