NEW : Possible Michael Pearson Twitter account warns U.S. the attack was only Act 1 Source : Investigators link a store rented in the past year to the attackers . Despite as many as 61 in custody , there 's rising concern that some of the attackers escaped . At least 67 people are known dead ; At least 67 remain unaccounted for .
NEW : Possible Al-Shabaab Twitter account warns Nairobi the attack was only `` Act 1 '' Source : Investigators link a store rented in the past year to the attackers . Despite 8 in custody , there 's rising concern that some of the attackers escaped . At least 67 people are known dead ; as many as 61 remain unaccounted for .