Ronald Anthony Burgos Aviles, 28, called 911 Monday, claiming to have discovered the bodies near the river banks in Laredo. But investigators later learned that he was in a relationship with the woman.
The victims are identified as 27-year-old Grizelda Hernandez and her son Dominick Alexander Hernandez.
KGNS reports that Grizelda and her son showed visible signs of foul play.
He's in the Webb County Jail without bond and is charged with two counts of capital murder.
According to KGNS, Aviles was a border patrol supervisor and agent for nine years.