The interrogation came the same day authorities searched the ex-President's home in Sao Bernardo do Campo, the Lula Institute in Sao Paulo, his son's home and others, federal police in the city of Curitiba told reporters.
Lula da Silva was questioned for three hours at a Sao Paulo airport before being released. He then headed to an office of his Workers' Party in the same southeastern Brazilian city, where supporters sang his name.
Police said the activity, involving about 200 officers and 30 federal revenue service auditors, is part of a broader inquiry into corruption and money laundering tied to Brazil's state-owned oil company, Petrobras. Federal prosecutors allege that Lula da Silva benefited from a bribery scheme involving the oil company while President and after leaving office.
Authorities think construction companies made large payoffs to Petrobras executives and politicians in exchange for lucrative contracts. Among other things, investigators are looking into whether these funds were used to pay for a luxury triplex and a country home believed to have been used by Lula da Silva. They're also investigating any payments, donations to the Lula Institute and speaking fees made by construction firms to the former President.
The Lula Institute responded defiantly Friday to what it called authorities' "arbitrary, illegal and unjustifiable" actions, insisting that Lula da Silva "never concealed assets or received undue advantage" before, during or after his presidency.
"The only (purpose) ... is to subject the former President to public embarrassment," the Lula Institute said of the anti-corruption investigation known as Lava Jato. "It is not Lula's credibility that is compromised when its leaders turn to a political target in the most fragile pretext."
This feeling was echoed by the Workers' Party, known as PT in Brasil, which referred to its longtime standard bearer as a "political prisoner" and urged people to stand by him.
The party tweeted, "We cannot let this go."
From peasant to President
It's too early to tell what will happen to Lula da Silva next, including whether he'll be arrested and put on trial. Still, there's no doubt the intense, extensive probe threatens the storied legacy of one of Brazil's most famous and most revered politicians.
Lula da Silva served two terms, from January 2003 to 2011, as Brazil's President. This put him in charge of the South American nation as its economy soared and it made historic breakthroughs, like winning the rights for Rio de Janeiro to become the first South American city to host an Olympics. Those Games
will happen this summer.
His former chief of staff and energy minister, Dilma Rousseff, earned Lula da Silva's support and took his place as President five years ago. If not for constitutionally mandated term limits, he could have won again: Lula da Silva left office with an approval rate upwards of 80%, not to mention many fans elsewhere in Latin America.
His appeal rested, at least in part, on his life story as a man who'd gone from poverty to the top of Brazilian society.
Born to a peasant family in an impoverished part of northeastern Brazil, Lula da Silva moved to Sao Paulo to work at a factory before making a name for himself as a union leader.
He helped found the leftist Workers' Party in the early 1980s, then successful ran for a seat in Brazil's national legislature later that decade. Lula da Silva lost his first three presidential runs before finally breaking through with a win in 2002's election.
Since leaving office, the man widely known as simply Lula underwent chemotherapy to treat a malignant tumor
in his larynx. It was announced, in February 2012, that this cancer was in remission.
These health battles aside, Lula da Silva remained a popular force in Brazilian politics. Just this past weekend, he said he wouldn't rule out running for President in the next election.
Lula da Silva: 'The snake is more alive than ever'
Now, the 70-year-old's political future is in doubt, as is whether he will stay out of jail.
According to Brazilian state news, authorities are looking into 20 million Brazilian reals ($5.4 million) in donations to the Lula Institute and 10 million reals in speaking fees.
A small number of companies -- Camargo Correa, Odebrecht, UTC, OAS, Queiroz Galvao and Andrade Gutierrez -- accounted for 60% of the donations and 47% of the speaking fees, the report notes. These aren't small companies. Rather, they are some of Brazil's biggest, with lots of projects nationwide and available money, some of which routinely goes to the country's political parties and players.
Lula da Silva isn't the only one affected. The investigation also casts a cloud over Rousseff, who has not been implicated in corruption, though authorities do allege the Workers' Party, which she also belongs to, did benefit.
The Lula Institute predicted Friday's police actions would backfire by causing Brazilians to lose trust in the government.
"The violence this morning -- unfair, unjustifiable, arbitrary and illegal -- will be repudiated by all ... who have faith in the institutions and the rule of law in Brazil," the nonprofit said, alleging not physical but rather symbolic harm to Lula da Silva and his allies. "... It is a violence against citizens (who) recognize Lula as the leader who united Brazil and promoted the highest social mobility in our history."
Lula da Silva told reporters that police treated him "courteously," though he expressed more anger that his friends and family had been caught up in the ordeal. He alluded to "the upper classes (who) want to bring (poorer) people back down," but he insisted that neither they nor he can be counted out.
"If they wanted to kill the snake, they missed the head and got its tail instead," the former President said. "Now, the snake is more alive than ever."