Some of the emails had the subject line, "Think Twice." They were sent from a spoofed email address. The sender claimed to have had an associate plant a small bomb in the recipient's building and said the only way to stop him from setting it off was by making an online payment of $20,000 in bitcoin.
This turned out to be a real threat, and not extortion. 
( z1 turn-out :ARG1 ( z2 and :op ( z3 threaten :ARG1 ( z4 this ) :ARG1-of ( z5 real ) ) :op ( z6 extort :polarity - ) ) )