Maybe letting him out early was a bad idea

Who was the London terrorist who killed two:

Khan was one of nine members of an al-Qaida-inspired terror group convicted of plotting to bomb the Stock Exchange and build a terrorist training camp in Pakistan that was disrupted by MI5 and the police. He is also understood to have been a supporter of al-Muhijaroun, the extremist group which scores of terrorists were involved with, according to the anti-extremism group Hope Not Hate.

So he had a conviction for an attempted terrorist attack. So what was his sentence:

He was originally given an indeterminate sentence, with a minimum term of eight years in February 2012. This was replaced by a 16-year fixed-term sentence and an extended period on licence by the court of appeal in 2013.

So his sentence was for 16 years. But they let him out after seven.

Why?

Two people are dead because they did.

The irony is he started the attack after attending a conference on rehabilitating offenders!