An undercover cop in an electric wheelchair raised no suspicions as he made drug buys in downtown St. Paul.

The undercover officer bought drugs from more than 140 people over three months.

Ramsey County Attorney Susan Gaertner says as of Monday, 108 people had been charged, and 50 to 60 more cases were under review.

The drug buys were mostly in the area surrounding the Dorothy Day Center, a homeless shelter across from Xcel Energy Center, which will host the Republican National Convention in September. But Police Chief John Harrington says the undercover operation wasn't done in response to that event.

The downtown crackdown — dubbed Operation Gridlock — was a follow-up to last year's Operation Shamrock, which targeted dealing at St. Paul bus stops.