More details emerge about the victims
The names and pictures of the 15 men, two women and one child who were killed were released on Friday.
Seven people died at the Just-in-Time bowling alley, eight were killed at Schemengees Bar and Grille, and three died at hospitals, according to police.
A number of parents and children were at the bowling alley for a children's bowling league - including the youngest victim 14-year-old Aaron Young. His father Bill Young was also killed in the attack.
The eldest was 76-years-old Bob Violette - a retiree who was coaching the youth bowling league and was described as devoted, approachable and kind.
The Maine Educational Centre for the Deaf said the shootings killed at least four members of their community.
Other victims include father-of four Joshua Seal, who was described by his wife as the "world's best father", and part-time bowling alley worker Tricia Asselin.
Local councillor Leroy Walker told news outlets that his son, Joe, a manager at the bar, died going after the shooter with a butcher's knife.
Another victim Peyton Brewer-Ross was a dedicated pipefitter whose death leaves a gaping void in the lives of his partner, young daughter and friends, members of his union said.
Thirteen people were also wounded.
Photos of the victims were posted on a board behind Maine Department of Public Safety Commissioner Michael Sauschuck at a press conference on Friday as he read the names. A moment of silence followed.
The city held an online vigil on Friday night with local clergy members, prayers and music.
Locals expressed their shock and pain in chat postings, describing themselves as angry, grieving, tired and heartbroken. Those watching at home were urged to light candles.
The attack was the worst mass killing in Maine's history.