One group of suspects detained in the slayings Wednesday at a publishing house that distributes Bibles told investigators they carried out the killings to protect Islam, a Turkish newspaper reported.
The attack added to concerns in Europe about whether this predominantly Muslim country — which is bidding for EU membership — can protect its religious minorities. It also underlined concerns about rising Turkish nationalism and hostility toward non-Muslims.
"We didn't do this for ourselves, but for our religion," Hurriyet newspaper quoted a suspect as saying. "Our religion is being destroyed. Let this be a lesson to enemies of our religion."
The paper did not name the suspect. Local media said the suspects were students, and that the residence where they were staying belongs to an Islamic foundation.
On Wednesday, police detained four youths, aged 19-20, as well as a fifth who underwent surgery for head injuries after he apparently tried to escape by jumping from a window at the Zirve publishing house in the central city of Malatya.
Malatya Gov. Halil Ibrahim Dasoz said another five suspects, detained Thursday, were of the same age as those taken into custody on the day of the attack.
He did not say whether the group detained on Thursday had been at the scene of the attack, saying only that they had been picked up at "various locations."
The three victims — a German and two Turkish citizens — were found with their hands and legs bound and their throats slit at the publishing house. Police went to the scene after receiving calls about a fight, Milliyet newspaper reported.
The five suspects detained Wednesday had each had been carrying copies of a letter that read: "We five are brothers. We are going to our deaths. We may not return," according to the state-run Anatolia news agency.
Foreign Minister Abdullah Gul said the attack had hurt his country's image abroad, and was aimed at "Turkey's peace, Turkey's tradition of tolerance and Turkey's stability."
Prime Minister Recep Tayyip Erdogan described the attack as "savagery."
The German and one of the Turkish victims were found dead, and the third victim died in a hospital, Malatya Governor Halil Ibrahim Dasoz said. The German man had been living in Malatya since 2003, he said. Anatolia identified him as 46-year-old Tilman Ekkehart Geske.
It was the latest in a string of attacks on Turkey's Christian community — which comprises less than 1 percent of the 70-million population.
In February 2006, a Turkish teenager shot a Catholic priest dead as he prayed in his church, and two other Catholic priests were attacked later that year. A November visit by Pope Benedict XVI was greeted by several peaceful protests. Earlier this year, a suspected nationalist killed Armenian Christian editor Hrant Dink.
Authorities had vowed to deal with extremist attacks after Dink's murder, but Wednesday's assault showed the violence was not slowing down.
German Foreign Minister Frank-Walter Steinmeier condemned the attack "in the strongest terms," and said he expected Turkish authorities would "do everything to clear up this crime completely and bring those responsible to justice."
German Chancellor Angela Merkel's Christian Democrat Party — which opposes Turkey's bid to join the EU — said the attacks showed the country's shortcomings in protecting religious freedoms.
"The Turkish state is still far from the freedom of religion that marks Europe," the party's general secretary, Ronald Pofalla, said in a statement.
Turkey began EU membership negotiations in October 2005 but talks have stalled over Turkey's refusal to formally recognize EU-member Cyprus. The country is under intense pressure to improve human rights and to expand religious freedoms and free speech as part of its membership bid.
A group of 150 lit candles and unfolded a banner that read "We are all Christians" in downtown Istanbul to protest the attack and show solidarity with the Christian community. But there was far less public outcry than with Dink's murder, which was followed by widespread protests and condemnations. More than 100,000 people marched at Dink's funeral.
Malatya is known as a hotbed of nationalists, and is also the hometown of Mehmet Ali Agca, who shot Pope John Paul II in 1981.
The Zirve publishing house has been the site of previous protests by nationalists accusing it of proselytizing, Dogan news agency reported. Zirve's general manager said his employees had recently been threatened.