DeMarco is a minor character in Syphon Filter 3. He appears in Teresa Lipan's flashback during her time as an ATF agent in the early 1990s. In this time, DeMarco was an ATF agent working alongside Teresa Lipan and ATF Special Agent Kelly. DeMarco and the ATF were sent to investigate the FBI discovery of a survivalist militia compound and a satellite impact site near Paradise in northwestern Montana. However, as Teresa was doing her recon operation, DeMarco was captured by the local survivalist militia in Dead Man's Gully somewhere in the mountains of Paradise. When ATF command reported that Agent DeMarco was last seen in Dead Man's Gully and failed to report back, Teresa reported that Dead Man's Gully was near her location and that she was on her way there. Teresa later found him and as she was approaching him, DeMarco warned Teresa that there is an ambush. Teresa then eliminated the militia who attempted to ambush her and kill her. DeMarco was later untied by Teresa and proceeded to get out of there. His whereabouts are unknown but it is presumed that he is still alive.