significant purchases

Since the RIO offer there have been significant purchases of RIV shares @ $17. On 29 Dec over 1M shares were made XT at $17 and today there were 2 separate 50,000 XT purchases @ $17. These are significant purchases. Why would you purchase above the RIO offer of $16? IMO either Tata or another miner/steel company is purchasing to obtain a position in RIV. RIO needs > 50% to succeed. Tata already has 24%. So my guess is the Indians are buying to secure a block of shares (Tata and others) ahead of a RIO controlling interest. As always DYOR.