The shooter opened fire on people outside the building, belonging to the immigration authority ICE, from a nearby roof on Wednesday.
A person who was in the custody of the authorities was killed, announces the US Department of Homeland Security after previously incorrectly stating that there were two fatalities.
The two injured people were also detained. They are being treated in hospital with serious injuries.
No government employee was injured, according to the federal police FBI.
The suspected shooter is dead. He shot himself, writes Kristi Noem, minister for homeland security, on X.
The FBI is investigating the shooting as a "targeted act of violence", they state during a press conference. The motive is still unclear but according to the federal police, messages directed against ICE were found on the ammunition that was discovered. FBI Director Kash Patel has published a picture on X of ammunition where it is written "anti-ICE".
ICE, Immigration and Customs Enforcement, is a US federal police authority with the task of protecting the US against cross-border crime and illegal immigration. The authority has been provided with a record budget to be able to carry out President Donald Trump's promised mass deportations of undocumented migrants in the US.
