After the Argentine coup d’état on 24th March 1976, repression against the Montoneros political organisation intensified, as its armed guerrilla movement became increasingly fragmented.
Under these circumstances, many Montonero members left Argentina to establish themselves in different countries in Latin America and Europe. Several militants linked to the movement- some of whom were joined by their families- settled in Uruguay as exiles and refugees.
In July 1976, the Argentine and Uruguayan intelligence services exchanged and distributed a list of Argentine citizens linked to the Movimiento Peronista Montoneros (Peronist Montoneros Movement). The following year, in 1977, the coordinated operations between members of the Argentine Army and Uruguayan Army deepened in the context of Operation Condor.
On 16th November 1977, the Montonero militant, Oscar De Gregorio was arrested at the Port of Colonia (Uruguay) by officers from the National Naval Prefecture (PNN). He was imprisoned at the clandestine torture and detention centre run by the Uruguayan Naval Fusiliers Corps (Fusileros Navales, FUSNA) at the Port of Montevideo. There, he was interrogated by agents from the Uruguayan FUSNA and the Argentine Escuela de Mecánica de la Armada (Naval Mechanics School, ESMA). He was subsequently transferred to Argentina, where he then disappeared.
On 15th December 1977, a series of operations were carried out by the Dirección Nacional de Información e Inteligencia (National Directorate of Information and Intelligence, DNII) and by the Uruguayan Servicio de Información de Defensa (Defence Information Service, SID) in the neighbourhood of Lagomar (Canelones Department, Uruguay). These operations led to the capture and death of several Argentine nationals and their children.
On 16th December, a fourth operation took place, which included the detention of the famous Argentine pianist, Miguel Ángel Estrella, together with three other people.