Fire investigators are testing a substance found in an Long Island apartment where a deadly blaze killed a mother and three of her children.
    
They want to see if a liquid accelerant was used to set the fire Thursday. The substance found in the apartment was sent the federal Bureau of Alcohol, Tobacco, Firearms and Explosives lab in Maryland.
    
The county fire marshal has labeled the fire in Lawrence, N.Y., as suspicious.
    
The building's ground floor was occupied by a coin-operated laundry. But there was no fire damage to that business, which was closed when the blaze was reported around 5:30 a.m.
    
Investigators are focusing attention on a stairway leading to a pair of second-floor apartments where 12 people lived. Eight people survived the flames by jumping out second-story windows because the stairway was filled with flames.