Adam Curtis Williams, 33, was identified as the man who allegedly drove the New Hampshire couple's truck into Mexico on October 21, Kleberg District Attorney John Hubert said.
Michelle Butler, 46, and James Butler, 48, of Rumney, N.H., were found buried in a shallow grave on October 27 and 28 on South Padre Island, Texas.
The couple was traveling around the country with their RV and their truck. Relatives reported the disappearance of Butler. Their truck and camp vehicle were also missing.
The Butler's death was judged a homicide last week, the sheriff's office said.
Williams is currently wanted for crime theft.
Sheriff's deputies in Kleberg are asking anyone with information about the incident or Williams' whereabouts to come forward.
