When funds or institutions buy large amount of shares, a strategy they use is having their broker buy based on VWAP. Buys take place throughout the day but get posted as one trade at the average price. Sometimes the trades post after the close. The second scenario is the trade is pre-arranged at a certain price and executes on the close or just posts late.
there are usually large trades that occur as the market closes.
News 
Market Data 
Discover 
