(CNN) London Bridge attacker, Usman Khan's longtime lawyer Vajahat Sharif told CNN he was "completely shocked" that his former client carried out Friday's attack as he had seen signs from him over the years that he wanted to veer away from radicalism.

Sharif says he began representing Khan when he was charged in 2010 in connection with a plot to attack the London Stock Exchange. Khan was in his late teens at the time. "I didn't feel he understood with necessary depth the ideology he was following, and I didn't want it to become his life," Sharif said.

A letter obtained by CNN shows Khan writing from prison in 2012 asking to join a deradicalization course. Sharif confirms his team received the 2012 letter and had advised his client to write it with the hopes that he could meet with a specialist intervention consultancy based in the United Kingdom that focuses on rehabilitating individuals convicted of terrorist offenses.

In the letter Khan writes, "As you are fully aware of my offence, which is a terrorism offence. It relates more to what I intended and the mindset at that time, also the views I carried. Which I realize now after spending some time to think were not according to Islam and its teachings."

A letter, written by London Bridge attacker Usman Khan, in October 2012.

But Sharif said limits on access to prisoners such as Khan prevented his client from being able to meet with a consultant from the rehab program.

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