It's chilling new surveillance video obtained by INSIDE EDITION of the accused Boston bombers working out at a gym just three days before the terrorist attack.
Tamerlan actually vaults into the ring at the mixed martial arts center in Boston on April 12th. The bombings took place 72 hours later on April 15th.
In the video Tamerlan looks relaxed and can be seen skipping rope with considerable skill, moving up and down and side-to-side like the expert golden gloves boxer he was.
Then, 19-year-old Dzhokhar climbs into the ring, but he has trouble keeping up the baggy shorts that look too big for him.
Tamerlan moves around the ring like he owns it, stretching, touching his toes, kicking, lunging and punching the air.
Dzhokhar's workout appears more half-hearted and he winds up standing in a corner of the ring while his brother prances around. Finally, Tamerlan jumps out of the ring in one hop, leaving his brother behind.
Three days later, the brothers would be captured on surveillance video at the Boston marathon finish line.
Meanwhile, Aerosmith's Steven Tyler led an all-star lineup Thursday night at the Boston Strong concert to raise money for the bombing victims.
It's another step in healing from the tragedy that these two brothers are accused of causing.