Agents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives are assisting investigators on Long Island following an apartment fire that killed a mother and three of her children.

A Nassau County police spokesman confirmed Friday that arson investigators are receiving assistance from their colleagues on the federal level.
    
The county fire marshal has labled Thursday's fire in Lawrence, N.Y., as suspicious.
    
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.
    
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.