The Zirve publishing house has been the site of previous protests by nationalists accusing it of proselytising in this 99 per cent Muslim but secular country, the news agency said.
Zirve's general manager told CNN-Turk television that his employees had recently been threatened.
"We know that they have been receiving some threats," Hamza Ozant said, but could not say who made the threats.
The manner in which the victims were bound suggested that the attack could have been the work of a local Islamic extremist group, said commentators.
CNN-Turk said police were investigating the possible involvement of Turkish Hezbollah - a Kurdish Islamic organisation that aims to form a Muslim state in Turkey's Kurdish-dominated southeast.
Turkish Hezbollah - which has been known to “hog-tie” its victims while torturing them - takes its name from the better-known Lebanon-based Hezbollah, but has no formal links to it. Turkish authorities recently said they were witnessing an increase in the group's activities.
Of Turkey's 70 million people today, only about 65,000 are Armenian Orthodox Christians, 20,000 are Roman Catholic and 3,500 Protestant - mostly converts from Islam. Another 2,000 are Greek Orthodox Christians.