Expositor's Bible Commentary Commentary John 11:31

"The Jews then who were with her in the house, and were consoling her, when they saw Mary, that she rose up quickly and went out, followed her, supposing that she was going unto the tomb to weep there." — John 11:31 (ASV)

The Jews knew something was afoot when Mary left so hastily. Since they had come to mourn with the sisters, they thought it only fitting to follow her, supposing that she was going to the tomb.