Private news agency Dogan, quoting morgue officials, reported that di Marineo had been strangled with a rope. The state-run Anatolia news agency said the suspect had strangled her with his bare hands.
Police tracked down the suspect when he switched on di Marineo's mobile phone some time after her March 31 disappearance, an Italian Embassy official said. The official spoke on condition of anonymity because he was not authorized to give information on the police investigation.
Authorities said the suspect has not been charged and it was not immediately clear if he had an attorney. The suspect has a prior theft conviction, the Anatolia news agency reported.
The artist, also known as Pippa Bacca, began hitchhiking March 8 with a friend from her hometown of Milan to the Palestinian territories as part of her "Brides on Tour" project calling for peace in conflict areas. The two separated near Istanbul with the aim of reuniting in Beirut, Lebanon. Di Marineo was last seen in Gebze.
"Her travels were for an artistic performance and to give a message of peace and of trust, but not everyone deserves trust," her sister, Maria, was quoted by the Italian news agency ANSA as saying in Milan.