Opposition presidential hopeful Bernard Ntaganda "was taken in to answer some accusations," police superintendant Eric Kayiranga said.
Other charges against Ntaganda include setting up rebel groups, causing ethnic divisions, and gathering people without permission.
Kayiranga also confirmed the Thursday evening shooting of opposition journalist Jean-Leonard Rugambage.
"He was killed in front of his house when he was going home at 10 pm," he said, adding the "unknown gunman" responsible for the attack had vanished.
Witnesses said Rugambage, the acting editor of the newspaper Umuvugizi, was shot by two men who then fled in a car.
Rugambage had accused the Kagame regime of attempting to assassinate dissident general Kayumba Nyamwasa in Johannesburg on 19 June.
The paper's exiled editor said there was no doubt as to why Rugambage was killed.
"It's clear that Jean-Leonard was killed following his investigations into last week's assassination attempt," Jean Bosco Gasasira told media monitoring group Reporters Without Borders (RWB).
RWB said it was the first murder of a journalist in Rwanda since 1998.