Najib has consistently denied any wrongdoing.
Najib's lawyer Harpal Singh Grewal says they didn't find anything incriminating, "just some personal possessions, couple of handbags, some presents, things like that".
A photo of Najib sleeping on a couch went viral, prompting criticism of the raid.
Police said that the search was not over.
However, Eric Paulsen, executive director of Lawyers for Liberty, said: "This is a real crime, involving billions in public funds, not some frivolous social media or sedition comments that led to a house raid".
Asked about the searches at a press conference, Prime Minister Mahathir said it was a police matter in which he had little information.
Researchers may have figured out toxic, lime green lizard blood
He notes that elevated levels of biliverdin have been found in some fish, and they may also explain the green blood in some frogs. They apparently find being green so easy that even their blood is green.
As a result of the surveillance, Najib and his wife have been barred from leaving the country for now.
Since coming to power, Mahathir has removed the attorney general who cleared Najib of offence, replaced head of the anti-corruption head and declassified an 1MDB financial report.
A declassified document compiled by Gani revealed a complex network of worldwide money laundering involving sums much larger than previously thought.
Mahathir has said there is sufficient evidence to investigate the 1MDB scandal. The department had seized assets bought with the 1MDB funds, including Van Gogh paintings, jewelry and properties in NY.
"At the same time, I hope that such actions also take into account that until today, Dato" Sri Najib, a former prime minister, has served the country immensely since becoming a "wakil rakyat' since he was 22, has not been charged in court and thus, should be accorded the appropriate treatment in line with the principle "innocent until proven guilty" which I am sure is also shared by Pakatan Harapan, who have been championing democracy all this while".