Sgt. Troy Price said in a news release that Linda Smith, 63, and Kalista Andino, 21, had been taken into custody, and more arrests were expected. Details of the allegations against them were not immediately disclosed.
Smith and Andino were booked into the Clark County Jail. It was not known whether they had obtained lawyers.
A white pickup truck reportedly ran down two women, Irina Gardinant, 28, and Raisa Mosh, 45, in a crosswalk on Northeast Vancouver Mall Drive on Sunday. Mosh's 12-year-old son suffered minor injuries.
Following the collision, Vancouver police launched a public campaign to find the white pickup, as well as a black pickup that drove by shortly afterward.
A white pickup with front-end damage was discovered at an apartment garage nearby, and the owner has refused to cooperate.
"The problem with this case is we have quite a few people that are close to the suspect . but everyone by and large would not provide us with any assistance or information," The Columbian newspaper quoted Price as saying.
The suspect, he said, is "basically telling the whole circle of friends not to cooperate, not to speak to police." But if they refuse to cooperate, they could find themselves facing charges as well, he said.
"I don't think everybody's thinking clearly," Price said. "People are letting allegiance override what should be a common sense and moral thing to do."