Palermo, May 20 - The Palermo appeals court on Monday gave prosecutors the first green light to have Italian President Giorgio Napolitano testify in a trial on alleged secret negotiations between the Mafia and the Italian State in the early 1990s, according to a witness list made public on Monday. The list of almost 200 prosecution witnesses is being reviewed by a panel to ensure that admissible evidence goes before the judges in the case that is slated to proceed on May 27. The panel may ultimately rule out calling the president to testify. It has been alleged that State officials entered negotiations with Cosa Nostra in a bid to stop attacks after a long campaign of violence that culminated in two bombings in 1992 that killed anti-Mob prosecutor Giovanni Falcone, his wife, fellow prosecutor Paolo Borsellino, and several bodyguards. The complex case has seen numerous twists and turns. Earlier this year, a judge in Palermo destroyed wiretaps of Napolitano, effectively ending a judicial clash that pitted the sanctity of the presidency against the duties of Mafia investigators. That came after a ruling last December by Italy's Constitutional Court ordering the Palermo prosecutors to destroy recordings of four conversations Napolitano had between late 2011 and May 2012 with Nicola Mancino, a former interior minister and Senate Speaker. Napolitano had successfully argued that the Italian Constitution forbids prosecutors from investigating the head of state unless he is suspected of high treason or attacking the Constitution itself. The wiretaps should have have been destroyed immediately, the president said. Mancino was charged along with 11 other people last July in relation to alleged negotiations to stop the series of Cosa Nostra bomb attacks in the early 1990s. Mancino is accused of perjury for saying he did not know about the negotiations. He denies this.