An official statement from the club read:
Millwall Football Club will do everything possible to assist the Football Association and the Metropolitan Police investigating the disorder that occurred during Saturday's FA Cup Semi-Final against Wigan Athletic at Wembley Stadium.
The Met confirmed after the match that they had made ten arrests with more expected to follow.
Millwall CEO Andy Ambler said: "Our position is clear. Anyone associated with our club found guilty of violent behaviour will be banned indefinitely from Millwall matches in addition to any punishment they receive from the authorities.
Having worked so hard to show the positive side of our club both on and off the field, we cannot allow the actions of a mindless minority to undermine that.
At this stage we are still in the process of establishing the full details of what happened in a section of the ground during the second half. When we have those facts at our disposal and the police have completed their investigations we may be in a position to comment further."
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The 52-year-old had previous convictions for violence but was not on the anti-terror watchlist.
In a statement Charlton Athletic said: Keith was a true hero who will be greatly missed by all the Charlton family and everyone at the club.
London and the worlds has united on Twitter in defiance of the West minster attack #prayforlondon #wearenotafraid