They made the statement after searching his home in the early hours of Friday morning and questioning his neighbors.
Manyurov, who was shot dead during the attack, opened fire on the FSB's main building in Moscow on Thursday evening, killing one FSB employee outright and wounding five others, including one civilian.
Russian investigators said in their statement on Friday that a second FSB employee had been seriously wounded in the same attack and had later died from his wounds in hospital.That took the death toll to two, excluding the gunman.