October 21, 2015 01:05 PM

A couple who had been married nearly 50 years were found murdered at a Hammond, Louisiana, rest stop on Monday, a police spokesman tells PEOPLE.

Denis and Suzanne Duplantier were discovered strangled to death in the back of their pickup truck hours after concerned relatives reported them missing from their Baton Rouge home.

“We are shocked and heartbroken,” family friend Molly Chesson Smith told The Advocate. “This will leave a hole in Baton Rouge for quite some time. This is a big one, a hole in a lot of hearts.”

Authorities believe the Duplantiers were initially victims of a home invasion. “We think the couple were kidnapped and taken in their own vehicle to Hammond, where they were dumped off in this parking lot,” the Hammond police spokesman says.

He credited OnStar with helping to locate the pair’s missing car.

The couple’s home showed no sign of forced entry, but the door was open and their safe was unlocked and missing various items, according to WWL-TV.

At a press conference on Wednesday morning, Baton Rouge police announced that they had taken a suspect, identified as 42-year-old Ernesto Llerena Alonso, into custody in Miami, Florida. He is charged with two counts first-degree murder and two counts of second-degree kidnapping.

Alonso knew the victims and did “odd jobs” for the couple around the house, Baton Rouge police said.

Hammond police confirm to PEOPLE that Alonso was arrested Wednesday morning.

Police are looking for one other suspect in the murder.

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