"What did Vittorio Arrigoni do to deserve death?" read the banner, which runs across a still photo of Arrigoni. It was probably photoshopped to show him dressed in a black t-shirt, Al-Qaeda's hallmark colour, sporting a black tattoo and holding a black hat.
"A criminal terrorist group killed the Italian who expressed solidarity with Gaza," read the caption beneath a second photo showing Arrigoni prostrate on the ground, praying to Allah, suggesting he may have converted to Islam.
The photos, banner and caption were published on the Al-Qaeda linked sites soon after messages from two Salafite groups in Gaza were posted to jihadist sites denying involvement in Arrigoni's killing.
After the Al-Tawhid Wal-Jihad and the Masada al-Mujahidin fi Falistin groups denied involvement in Arrigo's slaying on Friday, militant Palestinian group Islamic Jihad voiced condemnation of his killers saying "they have done Israel a favour".
"The killing of the Italian volonteer is a real crime. Arrigoni was killed in a way that is condemned by all religions," said the statement by Islamic Jihad quoted by Palestinian media.
Gaza's ruling Hamas also condemned Arrigo's murder and said he had been found hanged in a house north of Gaza City. Other reports was suffocated or strangled.
Arrigoni was reportedly murdered by the Tawheed and Jihad group, one of several extremist Islamic groups that operate in the Gaza Strip in opposition to the Hamas government.
After his abduction late on Thursday a video was posted on YouTube in which Arrigoni appeared blindfolded with a bruised face.
In the video, the kidnappers said Arrigoni had been taken hostage in order to secure the release of an unspecified number of their members detained by Hamas security forces, including a jihadist leader called Sheikh Hisham al-Suedani.
The kidnappers, who called themselves the Brigade of the Gallant Companion of the Prophet Mohammed bin Muslima, said they would execute Arrigoni if their demands were not met by 5:00 pm (1400 GMT) on Friday.
It was unclear why the militants killed Arragoni before the expiry of the deadline.
A native of Italy's northern Lombardy region, Arrigoni had been living in the Gaza Strip for much of the past three years and had been active in the Palestinian cause for nearly a decade.