About 3,000 Christians live in Gaza among 1.5 million Muslims and relations between two communities have generally been good.
"Muslim and Christian relations are very strong and will not be affected by such crimes committed by criminal elements," expressed Hamas in a statement Sunday, calling Ayyad's death a "murderous crime."
According to reports, a large delegation of Hamas leaders visited Ayyad's family and delivered condolences on behalf of the prime minister, Ismail Haniya. In a statement, Haniya condemned the killing and said Hamas "would not allow anyone to sabotage" Muslim-Christian relations.
"We are one people waging a single struggle for independence and freedom," expressed Haniyeh, according to Reuters.
The Popular Front for the Liberation of Palestine, a faction that enjoys broad support among Gaza's Christians, also issued a statement, calling the killing "a desperate attempt to sabotage the good social relations in Palestinian society and the friendly relations between Christian and Muslims."
And the Hamas-run Interior Ministry, which said the crime "will not pass unpunished," said it had launched an investigation and promised to bring Ayyad's killers to justice.
So far, there has been no claim of responsibility, but suspicion has been focused on Islamist extremists who have also previously targeted internet cafés and video stores.
In April, Ayyad's bookstore was firebombed during a wave of attacks by a shadowy Muslim "vice squad" on Internet cafes, music shops and other targets associated with Western influence.
The bookshop, which opened in 1999, sells Bibles and Christian literature despite a spate of threats and attacks against it. It is run by a Baptist group, the Holy Bible Society, dedicated to projecting a Christian presence in the Muslim region.
"We can't express the shock," said Suhad Massad, director of the society, according to The Scotsman. "We don't know who is behind this attack."
Palestinian lawmaker Hussam Tawil, who represents Gaza's Christians, said the Christian community and all of Gaza society are "feeling deeply shocked because of this awful, ugly crime."
He also said it's "too early" to talk about the motive of the crime, adding that doing so "might be dangerous."
Simon Azazian, a spokesman at the Bible Society's head office in Jerusalem, however, told AP that the organization felt Ayyad was killed for his Christian faith.
Issa, a 24-year-old Christian who went to pay his respects at Ayyad's home, echoed that sentiment, saying, "He paid his life for his faith, for his dignity, and the dignity of the Bible and Jesus Christ."
"I am terrified and cannot believe this has happened in Gaza," added Issa, declining to give his last name because of the tense atmosphere.
Ayyad reportedly left two young children and a pregnant wife.
