They are directly responsible. The Ottoman Turks were the ones who perpetrated the Armenian genocide at the former half of the 20th century, and they have refused to acknowledge it even until today. This does not, however, mean that there is no proof of this, and it certainly does not mean they should not acknlowedge it.
Considering that the Armenian Genocide ("massacre" is a polite and incorrect term) was an actual policy implemented by the Ottoman government, any attempt to say otherwise is completely ridiculous. It was an attempt at ethnic cleansing, and it's one of the most studied attempts at it, after the Holocaust, in recorded history.
The Armenian massacre was a tragedy of the 20th century and the Turks should stop denying it. It is time for both parties to accept the truth and have a reconciliation. In the future, the whole world should work together to make sure that genocide does not happen in the future.
Yes, the Ottoman empire was responsible for the Armenian massacre, because they relegated non-Muslims to second-class status and then massacred them. This was genocide and it was racist. The Ottoman empire lasted from around the 1300s until the early 1900s. They were the government or nation that was behind this unspeakable genocide.
The Ottoman Empire is responsible for the Armenian massacre because that empire instigated the slaughter of countless Armenians. History shows that this has been the case on more than one occasion, so we need to stop looking elsewhere to figure out what caused the Armenian massacre time and time again.