Arms allegedly smuggled into Iraq “may have been used against US forces”.
He said the findings would be referred to court for possible criminal investigation.
The incidents include a shooting outside Iraqi state TV which killed three guards on February 7.
The US state department relies heavily on private contractors to protect its diplomats and government personnel in Iraq because it lacks the means to do so itself.
Anne Tyrrell, a Blackwater spokeswoman, made no comment on Saturday morning.
The developments add to rising tensions between Iraq and the US following last Sunday’s shooting that killed at least 11 Iraqis and wounded 12 others.
American witnesses have said that the Blackwater security guards were responding to an attack, however many Iraqi witnesses told investigators the shooting was unprovoked.
In its defence, Blackwater has said its guards, who were guarding a US diplomatic convoy, were returning fire from armed men and acted appropriately.
Iraq‘s prime minister, Nuri al-Maliki, has called the incident a “crime” and his government has suggested that the US no longer use the firm in Iraq.
Iraqi officials initially ordered a ban on the company, but the US embassy resumed sending convoys out with Blackwater on Friday.
The killings have outraged many Iraqis, who resent the presence of armed Western security contractors, considering them as mercenary forces that abuse Iraqis in their own country.
Condoleezza Rice, the US secretary of state, spoke to al-Maliki via telephone on Monday, expressing regret for the deaths – asking that any action against the security firm be held off until further investigation.