Probably this Red RV6 which has been missing since March 2011.
Quote:
...On Sunday, March 13 (2011), the NPS received a report of an activated emergency locator transmitter (ELT) approximately 30 miles northwest of Grand Canyon Village. When manually activated, or automatically activated upon impact, ELT beacons send out distress signals. ...
... On Monday, March 14, the Coconino County Sheriff’s Office (CCSO) contacted the NPS about a missing person...
...With a wingspan of only 23 feet, the airplane may remain lost in the Grand Canyon for quite some time... or not.
Article at link has specific ID which is probably what the ME's office is attempting to confirm.

This sounds like one of the older 121.5 MHz ELT's, not one of the newer 406 models that has location info.