MASON CITY, Iowa (January 3, 2013)--Authorities have identified two of the three people who were killed when a medical helicopter crashed into a northern Iowa field as nurse Shelly Lair-Langenbau and paramedic Russell Piehl.

Witnesses told deputies that the helicopter burst into flames when it went down around 9 p.m. Wednesday just north of Ventura in Cerro Gordo County.

The aircraft was affiliated with Mercy Medical Center-North Iowa and had been headed to Emmetsburg to pick up a patient.

The pilot was not identified.

A Lewisville-based service company, Med-Trans Air Medical Transport, operated the helicopter.

Company officials didn't immediately return messages left Thursday by The Associated Press.

Sheriff Kevin Pals says the crash cause is being investigated.