PORTLAND, Maine (AP) — Evidence is being sought in the unsolved case of a killing that took place 20 years ago.

Police in Maine's largest city say 18-year-old Robert Joyal was stabbed to death April 4, 1998, during an altercation in the parking lot of a Denny's restaurant in Portland. He was a student at Gorham High School at the time.

Police say they interviewed dozens of witnesses and one man, Seiha Srey, was indicted on a murder charge. Charges against Srey were later dismissed, and no trial was held. He died in a 2007 shooting.

Police say they're looking for witnesses to the crime, or anyone who might have information but was reluctant to talk to police at the time of the stabbing.