Serbia's Appeals Court has overturned the acquittal of two former policemen accused of involvement in the 1999 execution-style slaying of three Albanian-American brothers and ordered a retrial, the war crimes prosecutor said Monday.

The court earlier this month accepted the prosecution appeal and ruled that "the state of facts had not been fully determined," the prosecutor's office said in a statement.

It was not immediately clear when the new trial against Sreten Popovic and Milos Stojanovic would start.

The former policemen were charged with "war crimes against prisoners of war" for handing over the three brothers — Illy, Mehmet and Agron Bytyqi — to members of a special Serbian police unit that subsequently shot and killed them in a training camp in eastern Serbia.

The two were acquitted in 2009 after the war crimes court concluded there had not been sufficient evidence for a conviction. The prosecutors at the time claimed that witnesses had concealed the truth about the killings in their trial testimonies.

The Bytyqis came to Kosovo from New York in 1999 to join the Atlantic Brigade of about 400 Albanian-Americans fighting with the ethnic Albanian rebels against Serbia's rule.

After NATO bombed Serbia to stop its crackdown on the rebels, the brothers strayed outside Kosovo's unmarked boundary. On June 26, 1999, they were arrested in southern Serbia and spent 15 days in a Serb jail for illegally crossing the border.

Upon their release, they were taken by the two Serb policemen to eastern Serbia and were summarily executed. Their bodies — bound and blindfolded — were discovered in a trash-filled mass grave in 2001.

No one has been charged with the shooting itself. Members of the former special police unit allegedly involved have refused to reveal any details or names of possible culprits.

The United States had expressed concern that no one has been punished for the crime.

Kosovo declared independence from Serbia last year, but Belgrade has refused to recognize the status.