Salem State University is paying tribute to alumnus and slain Massachusetts Institute of Technology police officer Sean Collier. The college is holding a ceremony Monday to honor Collier, who earned a criminal justice degree from Salem State in 2009. Authorities say Collier was shot and killed by Boston Marathon bombing suspects Tamerlan and Dzhokhar Tsarnaev on April 18. Collier is remembered on Salem State’s campus as a friendly, caring, and selfless person. Several classmates and professors as well as president Patricia Meservey are scheduled to speak at the ceremony on the lawn next to the campus police station. The university has established a scholarship in Collier’s honor, to be given annually to a Salem State student studying criminal justice.