The Jubilee line ground to a halt during rush hour on 6 March after a man armed with a knife was thought to have been at Canary Wharf station.
Commuters were held up as delays beset the line between London Bridge and Stratford shortly before 9am. The man is thought to have made his way from the Central line before boarding a Jubilee line train.
However, officers were unable to find him when they searched a train carriage at Canary Wharf.
A British Transport Police spokesperson said: "Officers were alerted to reports of a man carrying a knife on board a Central line train service on Friday 6 March, shortly before 9am.
"The man is thought to have travelled on a Jubilee line service to Canary Wharf . Officers searched a train at Canary Wharf but no one was found matching the description."
Police are no longer looking for the man as no crime has been committed, a spokesperson told IBTimes UK.