On the night of the bombing, investigators said a car left Rahamis home in Elizabeth, New Jersey, drove through the Lincoln Tunnel and arrived in Manhattan around 6:30 p.m. Surveillance video apparently shows Rahami walking down 23rd Street about 37 minutes before a blast ripped through the block. A short time later, he allegedly turned up on 27th Street where an unexploded pressure cooker bomb was found.
http://www.cbsnews.com/news/ny-nj-bombing-suspect-ahmad-rahami-video-pipe-bomb-backyard/
The federal complaint describes how he came to Manhattan about two hours before the first blast on West 23rd Street in Chelsea, but does not explain a three-hour gap from then to when he is believed to have left the city via the Lincoln Tunnel at approximately 11:30 p.m.
Investigators have been aided both by surveillance footage as well as tracking of his phone, which had no cellular service but used available Wi-Fi.
http://www.cnn.com/2016/09/22/politics/ahmad-rahami-timeline-details/