Investigators in Texas released a photo Monday of two persons of interest in the deaths of a New Hampshire couple. The deaths of James Butler, 48, and Michelle Butler, 46, are being investigated as homicides, the Kleberg County Sheriff's Office in Texas said.

James Butler and Michelle Butler

They were found in a shallow grave on Padre Island, near Corpus Christi. The couple had been traveling the U.S. since 2018, but in mid-October they abruptly went silent, and police said their truck and RV trailer crossed the U.S.-Mexico border without them, CBS News correspondent Meg Oliver reports.

Investigators said both vehicles were last seen on surveillance video between October 20 and 21 crossing the border, Oliver reports. The driver was not James or Michelle.

In a press conference Monday, Kleberg County District Attorney John Hubert said investigators don't have enough evidence to show that the two people seen in the truck are suspects. "At this point, we just know that they might have come in contact with the victims, and because of that we want to talk with them, but we've got no indication as to their role at this point," Hubert told reporters.

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Hubert said a man seen in the truck was wearing large-holed earrings. "If I could use stereotypes, I think they're probably local to the Corpus Christi area," Hubert said.

Two persons of interest are seen crossing the U.S.-Mexico border in an image released by the Kleberg County Sheriff's Office in Texas on November 4, 2019.

Investigators have been in contact with Mexican authorities, Hubert said. The Butlers most recently had worked as gate guards for oil rigs in Texas, checking vehicles in and out, said James Butler's sister, Deborah van Loon, of Rumney, New Hampshire, on Saturday.

They were in frequent contact with family and shared photographs of their trip on Facebook, she said. "We all loved what they were doing and they loved sharing it with us," said van Loon who described her brother as "an all-around really wonderful man."

He had retired from the Navy in 2010 and "loved to joke around about everything," she said. He came back to Rumney after he retired when his mother was dying of cancer, van Loon said. He met Michelle then and they married in 2015, she said.

The couple was likely headed to a part-time job in Fort Lauderdale, Florida, and due to arrive there in November to sell Christmas trees, van Loon said.