Hamas has good reason to be paranoid, Israel’s Shin Bet has an army of Palestinian spies.

GAZA (NYT) — Masked gunmen in Gaza summarily executed a man here on Friday as a suspected collaborator with Israel on the third day of its deadly aerial bombardments, shooting him multiple times and leaving his body beneath a billboard featuring a Hamas fighter holding a rocket.

The executed man, identified as Ashraf Ouaida, had a poster hung around his neck accusing him of cooperating with the Israelis in the killing of 15 Palestinian leaders.

Wael Mohammed, a taxi driver who was standing on the steps of the Aman Mosque in the Sheikh Radwan neighborhood of Gaza City, said that around 11:45 a.m. he saw a Jeep pull up on Al Jalla Street, from which two masked men dragged Mr. Ouaida to the dirt circle under the Hamas billboard.

“They took him out from the Jeep with his hands cuffed behind his back, they pushed him under the poster and fired three gunshots at his head from the back,” Mr. Mohammed said. “He was still alive. Then they set his cuffs free and turned him upside down and fired on him again.”

One of the gunmen, Mr. Mohammed said, hung a poster in which Hamas’s Al-Qassam Brigades claimed responsibility and cited Mr. Ouaida’s alleged crimes.

By noon, at least 100 men and boys, some carrying prayer mats, had gathered around Mr. Ouaida’s body, covering his bloodied head with a plastic sheet. He was wearing blue pants and a black zip-up sweatshirt and his feet were bare, and one dusty sandal sat by his hand. Another 15 minutes elapsed before an ambulance took him away.

The brazen nature of the execution suggested that Hamas, which governs Gaza, intended it as a blunt message to other possible collaborators with Israel, which is believed to have an extensive network of informants here as part of its underlying battle with the group. But the shooting evoked mixed feelings.

“There were kids and children on the street,” said the witness, Mr. Mohammed. “They should have executed him in a far place.”