(TNS) — Authorities at all levels have planned six months in advance of April 16, when the 122nd Boston Marathon race will take place. This year commemorates the fifth anniversary of the marathon bombings that left three dead and hundreds injured, and officials say their safety methods have adapted since that devastating day.

"I'm sure everyone can remember where they were, who they were with and what they were doing when the bombs exploded," said MBTA Transit Police Chief Kenneth Green at a security briefing in Boston on Tuesday. "It was that devastating to us."

"However with the passing of time human nature has its way of minimizing events that occur," Green added. "We cannot become complacent."

Officials across local, regional and federal law enforcement spoke on Tuesday to remind the public that while there are no credible threats to the marathon, spectators must remain vigilant in large crowds. Several officials repeated the mantra, "If you see something, say something." 

Marathon Monday attracts hundreds of thousands of spectators, on top of the 50,000 runners participating in the race. Police officials say between 7,500 and 8,000 public safety personnel will be situated along the race route, which spans across eight cities and towns. According to Massachusetts Emergency Management Agency Director Kurt Schwartz, 5,000 of those personnel will be uniformed and plain-clothed officers.

Massachusetts State Police Colonel Kerry Gilpin said there will also be a "significant number of undercover troopers" mixed into crowds on race day. "Certain parts of our security operation will not be seen by the public," Gilpin said. 

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