Sunday's arrest of Kaegan Jude Solet came after Terrebonne Parish deputies tied him to a stabbing attack that left four adults dead on Ashland Drive.
A minor found Saturday with apparent stab wounds was airlifted to an out-of-area hospital and remained in critical but stable condition, leading investigators to the nearby homes where the adult victims were discovered.
Two victims were found inside one residence and two more in a second structure on the same property; officials called the scenes very violent and said at least one victim was an elderly woman.
Lt. Blake Tabor said investigators believe Solet, the child and the four adults were connected and do not view the killings as random, though identities, relationships and a motive have not been released.
The sheriff's office said the case is the first quadruple homicide in the agency's history and remains an active investigation as detectives contact relatives and interview witnesses.