With the return of democratic rule in 1980, President Belaúnde reopened the university. The radical elements among the students and lecturers were quick to return, and by the mid-1980s the country's two main insurgent groups, Shining Path "(Sendero Luminoso)" and the Túpac Amaru Revolutionary Movement (MRTA), had a strong presence on campus. By the early 1990s, due to a strategic withdrawal by MRTA and the fragmentation of the other left-wing groups on campus, legal and illegal alike, Sendero Luminoso had the upper hand. This was in spite of operations such as that of 13 February 1987, when 4000 police officers conducted night-time raids at the dormitories of three state universities (including La Cantuta); 20 April 1989, when a joint force of police and army descended on La Cantuta University and San Marcos National University and arrested over 500 students on charges of subversion; or 22 May 1991, when, in response to a hostage crisis and rumors of an explosive device squirreled away on campus, Fujimori sent the army in to restore order at La Cantuta. Graffiti alluding to Sendero Luminoso and its leader, Abimael Guzmán, were painted over with patriotic slogans; students went about their business only after passing checkpoints and under close supervision from the armed forces; and the campus remained under military control for several years.