A much-publicized meeting between the journalist and State Secretary Ulrica Schenström eventually led to the resignation last week of the prime minister's aide.
Schenström had initially stressed that she was fully capable of carrying out her duties for the government's emergency response organization.
The Prime Minister said he had believed Schenström's account until the bill from her bar visit was made public. This showed that she and Pihlblad had between them spent 945 kronor on alcohol.
In a case led by chief prosecutor for corruption matters, Christer van der Kwast, the TV4 reporter is being investigated on bribery allegations after it was revealed that he had paid for the state secretary's drinks.
"Two police officers came to our reception at lunchtime and handed over a search warrant. They wanted the bill from the restaurant visited by Anders Pihlblad and Ulrica Schenström. We don't have that bill but we do have a slip from Anders's debit card," said TV4 spokeswoman Cecilia Giertta.
The station made a copy of the slip and gave it to the police.
"They then accompanied me up to the newsroom, which of course was very unpleasant. A prosecutor always has various options when carrying out an investigation and in this case he has chosen to raid an editorial office," said Giertta.
"We have lots of people up in the office who are there to provide sensitive information or be interviewed. Having two police officers come in is not exactly what people expect. Editorial offices are also somehow covered by the constitution," she added.
TV4 was not alone in expressing outrage at the chief prosecutor's decision to issue a search warrant.
"Van der Kvast clearly doesn't have much respect for press freedom," Jonas Morian, chairman of the Social Democratic Press Association, told The Local.
"I think in general he goes way too far. He seems to be driven by some sort of a higher moral cause," he added.
The Swedish Union Journalists was also furious at what it regarded as a serious breach of the constitution.
"The raid on TV4 constitutes an attack on the protection of sources enshrined in the constitution," said chairwoman Agneta Lindblom-Hulthén in a statement.
"It is a threat to the constitutional right of citizens to provide the media with anonymous information."