David Michael Miranda, the Brazilian partner of Guardian journalist Glenn Greenwald – Edward Snowden's go-to reporter for the dissemination of sensitive papers about the NSA's dragnet surveillance programs – has been released from custody. Metropolitan Police officers held the 28-year-old for almost nine hours, the maximum allowed before police are obliged to arrest someone under that legislation.

Miranda was released without charge but investigators seized his mobile phone, laptop, memory sticks, DVDs and a game console. Under the law, Miranda should get his kit back within seven days unless it is used as evidence in criminal proceedings.

Greenwald described the detention of his partner as a "failed attempt at intimidation".

"To detain my partner for a full nine hours while denying him a lawyer, and then seize large amounts of his possessions, is clearly intended to send a message of intimidation to those of us who have been reporting on the NSA and GCHQ," Greenwald told The Guardian.

The Brazilian foreign ministry issued a statement criticizing Miranda's "unjustified" detention. "The Brazilian government expresses grave concern about the episode that happened today in London, where a Brazilian citizen was held without communication at Heathrow airport for 9 hours, in an action based in the British anti-terrorism legislation," it said.

"This measure is without justification since it involves an individual against whom there are no charges that can legitimate the use of that legislation. The Brazilian government expects that incidents such as the one that happened to the Brazilian citizen today [are] not repeat[ed]."