In September 1991, rebel Serbs turned the factory into a detention camp through which about 10,000 Vukovar residents passed since the town's fall that November 18.
Society president Danijel Rehak said about 1,200 detained soldiers and civilians were estimated to have been killed at Velepromet.
"Croatia recognises that about 300 detained soldiers and civilians were killed in Serb concentration camps, but we think that about 10,000 detainees passed through those camps and that nearly one-third were killed," he said.
The 14th anniversary of the fall of Vukovar, held under the motto "Where Should I Look for My Son?" ended today as respects were paid to people killed at Ovcara.
Numerous delegations laid wreaths and lit candles at the monument at the farm.
On 19 November 1991, the Croatian government and the former Yugoslav People's Army (JNA) signed an agreement under which wounded soldiers and civilians from Vukovar's hospital were to be protected after the fall of the town. However, the next day Serbs forced out 261 wounded soldiers and civilians, killing 200 at nearby Ovcara. Sixty-one are still being traced.