Former NYPD Commissioner Ray Kelly said he's worried about a "copycat event" at the Boston Marathon Monday but believes officials have done everything possible to secure the race.

On ABC's "This Week" Sunday, Kelly suggested attendees will be more vigilant after last year's terrorist bombings, which killed three people and injured hundreds.

"It's a long distance to secure," he said, referring to the course, which travels through eight cities. "What you look for is abnormalities. What we used to say is you look at your world through the prism of 9/11. Now the officers, the spectators have to look at their world through the prism of what happened on April 15, 2013."

He added: "Authorities have done everything they reasonably can do to make this a safe and secure event. You can reduce the risks, but in a free and open society you can never totally eliminate it."