The investigators said they found elements of an explosive device in the apartment where they lived.
Russian news agencies reported that law enforcement agencies had arrested three people, but did not say if they were men or women.
The explosion claimed the lives of thirteen people and left another 55 wounded.
"Orders have been given to return (the evacuated) residents, everything is safe up to the seventh floor", he continued, adding that police were still searching the building's eighth and ninth floors. The Central Asian men were accused of recruiting other men from the region to join the Islamic state and other terror groups.
The committee, the nation's top criminal investigation agency, said investigators also found objects that would help advance the probe during a search of the home on St Petersburg's eastern outskirts.
"An explosive device was found, it has been defused", head of the city's Nevsky district administration, Konstantin Serov told reporters, according to Russia's TASS news agency.
Bomber 22-year-old Akbarzhon Dzhalilov blew himself up on a busy subway line on Monday, killing himself along with 13 others and wounding dozens of others. Earlier on Thursday, mourning continued in St Petersburg as the jittery city laid to rest the 14 people killed in the attack.
Thursday's arrest came a day after law enforcement agencies detained eight Central Asian migrants suspected of acting as recruiters for Daesh and Al Qaeda's Syria branch. The report said Russian investigators were trying to determine Dzhalilov's travels, but they had ascertained that the device used in the subway attack bore the hallmarks of "Syrian know-how", specifically traces of burnt sugar.
Victims' faces were ripped off when the the former sushi chef killed 14 by detonating a bomb on a crowded metro train in theRussian city on Monday. Her husband, Alexander Kaminskiy thanked everyone saying "The country and the entire world share our pain".
Blast victims lie near a subway train hit by a explosion at the Tekhnologichesky Institut subway station in St.Petersburg, Russia, Monday, April 3, 2017.