Thursday, July 18, marks 40 years since a gunman entered a McDonald's in San Ysidro in 1984, opened fire, killing 21 people and injuring 19 others. At the time, it was considered the largest mass shooting in U.S. history.

A witness, who now belongs to the San Diego Police Department, was shot five times by the attacker and, as a means of survival, used his shoelaces as tourniquets.

The San Ysidro McDonald's in California was eventually demolished and replaced by the Southwestern College Higher Education Center. In front of the new building, there is a monument featuring 21 hexagonal pillars representing each of the 21 victims.

The public can also attend a screening of Charlie Minn's documentary about the San Ysidro McDonald's massacre, called '77 Minutes', at the Reading Cinemas Town Square in Clairemont on Thursday at 6:30 p.m. There will be a Q&A session after the screening.