The New Hampshire man accused of killing his two children has entered a “not guilty” plea to murder charges. Authorities think Manuel Gehring shot his 14-year-old daughter and his 11-year-old son in New Hampshire on July 4th and that he buried them a day later, somewhere in the Midwest along Interstate 80. They’re still searching for the children’s bodies, in a zone along the interstate that includes part of Iowa. The FBI’s Larry Holmquist says they’re asking for the public’s help with another piece of evidence they think was taken from the suspect’s vehicle — a grey velour bench seat from a 1998 Pontiac Transport minivan they think was left along I-80 in Nebraska in a trash dumpster near a strip mall or shopping center. Credit card receipts indicate Gehring made a stop in Iowa as well as Nebraska. Holmquist says they think the seat was left along the roadside on July 6th or 7th, and part of the seat’s upholstery may be covered by a black plastic garbage bag. Anyone with information about the seat is asked to call the FBI at 402-493-8688.