Nancy Davis can be seen playing the accordion while her husband plays the guitar. As she sings, she lifts her arms in the air.
"Praise God, he's marching on he...he can still guide the darkest night," the couple sings in the video.
Police said anyone with information about the killing should call 956-787-8477
The shooting was similar to the attack on an American couple earlier this year while riding jet skis on Falcon Lake which straddles the U.S. and Mexican border.
David and Tiffany Hartley had driven their jet skis to the Mexico side of the lake on Sept. 30, 2010, but were ambushed on their way back to the American side. David Hartley was shot and fell off his jet ski and Tiffany, unable to pull him from the water, said she raced away under gunfire to save her life.
Hartley's body was never found and no one has been charged with his murder.
The area is infested with Zeta cartel members. The lead investigator on the Hartley case was later decapitated and his head was delivered to a military post near the U.S. border.
The Associated Press contributed to this report.