Cuarón shows the latter event in the film, during the sequence where Cleo and Sofia are out shopping for baby furniture.
That sequence came from the director’s childhood fascination with a photograph of that very furniture store during that event, which showcases onlookers witnessing the violence on the streets.
Both the Tlatelolco Massacre of October 2, 1968 and the Corpus Christi Massacre, also known as El Halconazo, of June 10, 1971 were instrumental to Roma’s actual narrative.