Of the 139 games officiated by Tim Donaghy during the past two NBA seasons, the opening point spread moved at least two points in 28 of them, or 20 percent, according to a source within the Nevada sports betting industry.

The trend, along with dramatic free-throw differentials in several of Donaghy's games, could provide important evidence to the NBA and federal authorities investigating whether the referee bet on games he officiated or furnished information to bettors as part of a possible point-shaving or game-fixing scandal.

Bookmakers pay close attention to the movement in betting lines because they often indicate that more money is being wagered on the team in whose favor the line moves. Two-point movements in NBA lines are common and can result from legitimate strategic factors such as the absence of a key player because of injury.