The blaze broke out on Columbia Street early Oct. 10, 2013, destroying two bridal stores, offices and the E.L. Lewis building, which belonged to one family for more than a century.
Fire crews from New Westminster, Delta and Burnaby fought the flames and there was at least one major explosion before the Lewis building collapsed.
City police say the major crime unit and forensic investigators from the city's fire department tried to determine what sparked the blaze.
But police say the investigation is now over and there will be no charges because they couldn't determine the cause.
New Westminster Councillor Jaime McEvoy said at the time that the blaze was the worst loss since the Great Fire of 1898 ravaged a third of the city's waterfront and downtown core.