You will see that the defenders of Catholic Christianity i.e. the Croats slaughtered Serbs in their Nazi camps.
By the way this is not to exuse the Serb actions in Vukovar in 1991 but what the Croats did from 1941-45 was genocide.
Heck, you want my friend who was a Serbian sniper based outside of Vukovar email me so you and a few others hear about what the Croats did?
"Between 3 May and 14 September 1991 members of Croatian armed units, as well as Tomislav MERCEP'S bodyguards arrested in Vukovar more than one hundred Serbs whom they subsequently locked up and tortured…"
Source: http://www.balkan-archive.org.yu/politics/war_crimes/vukovar/vukovar7b.html
(After Vukovar, Tomislav Mercep was involved in ordering the torture and murder of imprisoned Serbs in Gospic, according to the confession of Miro Bajramovic)
Serb reports here show the YPA didn't really do anything to help them and was passive while all this was going on, but in certain villages Serbs were able to save themselves from cleansing by putting up barricades. It appears only after Croats directly attacked the army or its members or with great show of force, barricaded them - or tried to -would actual fighting between Croat armed forces and the YPA start:
http://www.balkan-archive.org.yu/politics/war_crimes/vukovar/vukovar8.html
At the beginning of Croatian-Serbian confrontation in Vukovar municipality, YPA troops in the Vukovar garrison, acting upon the order of army leadership and Presidency of SW Yugoslavia, did not interfere in the conflict, but tried to act as a kind of impartial peace force. However, they were inconsistent in these efforts - for instance, they interfered on 2 May 1991 in Borovo Selo to save Croatian policemen, but stayed in the barracks when Croatian armed forces spearheaded forcible "cleansing" actions in Borovo Naselje (4 July) and Luzac (25 July) against the Serb population. Their members, with the exception of reserve troops from Vukovar, moved freely about the town even when Vukovar Serbs could practically no longer get out of their houses. The first major incident between YPA and armed members of the Croatian Democratic Union party militia occurred on 20 August 1991, when privates Dejan LAZAREVIC and Ljubo BRADULJEVIC were attacked in the Vukovar post office, where they used to come every day to pick up mail and money orders for soldiers in the barracks…
The new incident, which led to the first WA intervention against Croatian armed forces in Vukovar, happened on 25 August 1991, when Croatian soldiers, near their barricade on the way out of Borovo Naselje, planted an anti-tank mine under a YPA truck, the passage of which from Vukovar to Borovo Selo had been duly announced to the Croatian police…
Judging by this report, Vukovar was then for a few hours under full control of YPA units, which also took possession of the road towards Bogdanovci, the only way which the Croatian armed forces could use to enter and leave the city. However, at the request of the Croatian party, cessation of hostilities and return of YPA units to the barracks was arranged. This was a trap from which they could not get loose until 18 November 1991.
Descriptions of how Serbs were being killed and thrown in the Danubes along with a couple photos of Serbs dead in the Danube and their names: http://www.balkan-archive.org.yu/politics/war_crimes/vukovar/vukovar7c.html