When Brenton Tarrant approached the doors of Al Noor Mosque at the start of his mass killing, he was welcomed with the words "hello brother".

So was it just friendliness? Or was it something more - familiarity?

The Imam of the Mosque has revealed that a man he believes was Tarrant pretended to pray with worshippers in the weeks leading up to the March 15 massacre. One worshipper even says they hugged him.

Gamal Fouda says Tarrant even dressed up in traditional Pakistani clothes.

The Imam is convinced the Australian terrorist went there several times to check the layout of the building and to observe the schedule of the mosque members as he planned his attack.

Last month Tarrant pleaded guilty to 51 charges of murder, 40 of attempted murder and one terrorism charge.

Before the guilty pleas, Newshub couldn't report the Imam's comments about the terrorist visiting the Christchurch Mosque because they could hinder him getting a fair trial. But now we can report this exclusive story.