U.N. prosecutors told judges Monday that two former Serbian security officials who served under Slobodan Milošević helped train and equip ethnic Serbs to conduct brutal ethnic cleansing campaigns against non-Serbs in the 1990s Yugoslav conflict.

The re-trial of Jovica Stanišić, former head of Serbia’s state security service, and his subordinate Franko “Frenki” Simatović is the last major case at the U.N. war crimes tribunal for the former Yugoslavia in The Hague.

Both men have pleaded not guilty to crimes including murder and persecution as crimes against humanity. They are on provisional release in Serbia and did not attend the closing arguments in person.

In closing, prosecutors stressed that separatist Serb forces in Bosnia and in Croatia were totally dependent on Serbia under then-strongman President Milošević.

-This campaign was carried out by a variety of Serb and military, police and volunteer units that were trained and equipped by these accused- prosecutor Douglas Stringer said.

The prosecution is seeking a life sentence for both ex-associates of Milosevic, who stood trial for genocide and crimes against humanity in the Yugoslav conflict but died in his tribunal cell in 2006 before the verdict.

Stanišić and Simatović’s defence is due to respond later this week. Both men were acquitted in 2013, but appeals judges ordered a re-trial in 2015.

Stringer said the two men were vital cogs in a criminal enterprise led by Milosevic and the Serbian state, together with Serb forces in Bosnia and Croatia, to expel Croats and Bosniaks from Serb-claimed lands as Yugoslavia fell apart in the 1990s.

Judges have not set a date for the Stanišić and Simatović verdict.