Mexico City investigators will travel to the Gulf coast state of Veracruz to question its governor about the killing of a photojournalist, according to the mayor of the Mexican capital.
Miguel Angel Mancera said on Monday all lines of investigation remain open in the case, including possible political motives, and the investigative team will go to Veracruz on Tuesday.
Javier Duarte, Veracruz's governor, has told local media that he has no knowledge of the incident, which occurred on July 31 in a Mexico City apartment where four women were also slain.
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Ruben Espinosa, the photojournalist, had fled Veracruz recently, saying he feared for his safety due to his work covering protests.
Espinosa was tied up, tortured and shot in the head at an apartment in Mexico City.
The attackers also killed his friend, Nadia Vera, two of her roommates - a 19-year-old aspiring make-up artist and a woman believed to be from Colombia - as well as their 40-year-old housekeeper.
Vera had been active in organising protests for various causes in Veracruz.
Late last year, she had posted a video warning that if anything happened to her, it would be the fault of Duarte.
On Tuesday, authorities released security camera footage that appeared to show three men near the building where the killings took place.
They are seen leaving the scene calmly, and are believed to be suspects.
One suspect has been arrested and the crime scene showed some signs of violent robbery.
Thirteen journalists have been killed in Veracruz since Duarte took office in 2010.