Rimac has served five and a half years for involvement in the murder of an unknown man in Pakracka Poljana and for the extortion and unlawful arrest of three Zagreb Serbs in late 1991.
He told the court Mercep did not command his unit. He reiterated he did knot know who ordered him to go from Vukovar to Zagreb, Gospic and then Pakracka Poljana where, the indictment contends, civilians were brought, tortured and killed, of which Mercep, a former advisor to the interior minister, is accused as the unit's commander.
The witness said there was confusion, no military structure and many self-styled commanders.
Rimac said Mercep's function at the Interior Ministry was not operative but administrative, which referred to mobilisation and logistical supplies.
He said he never saw Mercep in Pakracka Poljana.
As for the Zagreb Trade Fair Centre's Pavilion 22, where the indictment contends civilians were brought, Rimac said it was a warehouse and that, contrary to media reports, there were no cages, a prison or barbed wire.
Rimac said he did not see prisoners in Pakracka Poljana, at the Zagreb Trade Fair Centre, or the Adolfovac lodge on Mount Sljeme overlooking Zagreb which the unit used.
Asked if he knew about Mihail Zec, the witness said he heard he was killed in Zagreb in December 1991 and that he knew nothing else about the murder. Rimac added that he was prosecuted in this case and that he was acquitted.
According to the media, Rimac confessed to the murder during an investigation but was acquitted because he had been interrogated without an attorney present.
Zec was killed outside his house in Zagreb on December 7, 1991, while his wife Marija and 12-year-old daughter Aleksandra were killed the same night near the Adolfovac lodge.
The trial resumes on Thursday.