Del Rosario was last seen in the vicinity of 30th Street and Colorado in Boulder, Colorado at 7:00 p.m. on August 28, 1987. He was driving a brown 1979 Datsun 280ZX at the time. He dropped a friend off and was supposed to pick up his girlfriend when she got off work at 7:30 p.m. He never arrived at her workplace and has never been heard from again. Del Rosario's car was later found abandoned in the parking lot of the now-defunct Crossroads Mall. There was a substantial amount of blood in the passenger compartment.

Del Rosario is originally from Miami, Florida, and his sister still lives there. He was attending the University of Colorado at the time of his disappearance. Authorities stated their investigation revealed he was possibly involved in drug distribution, moving cocaine from Miami to Colorado, but it's unclear whether drugs were a factor in his case. Foul play is suspected in his disappearance, which remains unsolved.