The parents and brother of a man being held as the suspected killer of Mexican actress Julia Marichal demanded his release on Monday.

Mauricio Marichal, the victim's nephew, was arrested on Dec. 5 and was ordered held in preventive detention for 30 days in connection with the death of the actress, whose decomposing body was found Dec. 2 in a water tank at her Mexico City home.

"Alfredo Mauricio Marichal Cancino has been deprived of his liberty in an unjust and unconstitutional manner ... while those really responsible for the murder go unpunished. We demand justice for Julia Marichal and Mauricio's immediate release," the suspect's father, Juan Alfredo Marichal, said in a statement.

Julia Marichal's relatives filed a missing person's report with the Center for Missing and Disappeared Persons, or CAPEA, but her body was found a few hours later at her residence in the Guayatla section of the Mexico City borough of Magdalena Contreras.

The suspect's father said that after learning that Julia was missing but before the body was found, he had asked his son to go to the artist's house to get "some documents of sentimental value for the family" in light of "suspicions that the house might be looted."

"All the details have been stated to prosecutors, they have come to my house, they have seen and photographed the documents, which were packed in a black bag and sealed with tape. I do not understand why my son is still being held in preventive detention. I demand his release," Juan Alfredo Marichal said.

Mexico City authorities are investigating reports of a dispute over work between Mauricio and Julia.

The suspect's mother, Maria Luisa Cancino, said in the statement that her son did not work for his aunt for pay, collecting only token amounts for a job that he did for purely "intellectual and sentimental" reasons.

"I learned from Julia about the work dispute that she had with Mauricio, but it was just that, a work disagreement that both exaggerated and is now being blown out of proportion" by officials, Maria Luisa Cancino said.

Julia Marichal was the daughter of Cuban actress Esther Martinez Peñate, who married Mexican writer Juan de la Cabada.

The late actress appeared in a dozen "telenovelas," or soap operas, including "Mundo de Juguete" (1974), and a number of films, such as "Las puertas del paraiso" (1971).

Marichal worked for several well-known directors, including Alejandro Jodorowsky and Ana Sokolov.

She was an advocate of black culture in Mexico and spent her last years trying to preserve the De la Cabada archives.