We're learning more about the 29-year-old father of three accused of plowing a pickup truck into pedestrians and bikers in lower Manhattan. The suspect's sister is now speaking out. This as the NYPD beefs up security across the city ahead of tomorrow's New York City marathon. ABC's erielle reshef is at the finish line with the latest. Good morning, erielle. Reporter: Good morning, Diane and Dan. New York City on high alert after that terror attack. Officials say this New York City marathon will have the tightest security ever in an effort to protect more than 50,000 runners and 2 million spectators here on Sunday. Unprecedented security spanning the route of the New York City marathon. Five days after the bike path terror rampage that killed eight people in lower Manhattan. We've also increased the number of observation teams and counter sniper teams. There will be substantial number of heavy weapons teams. Reporter: Officials say there is no specific threat. But remain concerned about international terrorists and domestic extremists potentially targeting the event. We're going through every possibility. Reporter: It comes as investigators say they tracked down sayfullo saipov's last known contact. Questioning the man who spoke to the terror suspect on the phone moments before his murderous truck attack. ABC news has also learned authorities in saipov's native Uzbekistan have interrogated his entire family in an interview with his sister she says investigators are still holding their father and uncle for questioning. Saipov's mother passing out in shock after hearing what her son had done. Three argentinean survivors of his ramming embracing as they remembered their childhood friends, the five mowed down seen here celebrating the 30th anniversary of their high school graduation just hours before their death. New York City still reeling but resilient as runners take their marks this marathon weekend. And we're already seeing canine officers here at the finish line of the marathon. Officials say there will be counterterrorism unit, snipers and helicopters keeping a wat watchful eye on the massive crowds but they're reminding everyone to be vigilant, Diane, Dan. We're certainly thankful for that protection thank you.