The three victims - a German and two Turkish citizens - were found with their hands and legs bound and their throats slit at the Zirve publishing house in the central city of Malatya, reported The Associated Press.
The publishing house has been the site of previous protests by nationalists accusing it of proselytizing in this 99-percent Muslim but secular country, reported Dogan news agency. Zirve's general manager said his employees had recently been threatened.
A group of 150 lit candles and held a banner that read "We are all Christians" in downtown Istanbul to protest the attack and show solidarity with the Christian community.
Prime Minister Recep Tayyip Erdogan condemned the attack, calling it “savagery” and said investigators were looking into whether there were other suspects or possible links with terror groups.
German Foreign Minister Frank-Walter Steinmeier also condemned the attack, and said he expected Turkish authorities would "do everything to clear up this crime completely and bring those responsible to justice."
Police detained four males, aged 19-20, and also suspect a fifth, who underwent surgery for head injuries sustained apparently in trying to escape by jumping from a window at Zirve, authorities said.
The five suspects 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.
EU membership in question
This recent attack has added to concerns in Europe about whether Turkey is ready to join the European Union.
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 party's general secretary, Ronald Pofalla, reaffirmed the place of religious freedom as a fundamental human right.
"After today's murders, the Turkish government must allow itself to be asked whether it is doing enough to protect religious minorities," Pofalla said in a statement. "The Turkish state is still far from the freedom of religion that marks Europe.”
Turkey's Christian community comprises less than 1 percent of the 70-million population. About 65,000 are Armenian Orthodox Christians; 20,000 are Roman Catholic and 3,500 are Protestant — mostly converts from Islam. Another 2,000 are Greek Orthodox.
.- Three employees of a publishing house that distributes Bibles were murdered Wednesday in the latest attack against Turkey's Christian minority.