Someone knows what happened that evening and I am urging them not to remain silent but to come and speak to us. Your information will be treated in the strictest of confidence.
Likewise I am directly appealing to the family members and friends of those believed to be involved - if you have slightest indication the person you know may have been involved in this incident I encourage you to get them to hand themselves into the police.
Failing to do so will result in my officers pursuing them.
More top news
Man who has barricaded himself in house for three days may have a stash of petrol and other explosives, police say.
Transport secretary Chris Grayling said MPs will decide this week about where to allow airport expansion in south east England
The Met Police has thanked residents in Northolt for their patience but has warned the armed stand-off could take time to resolve.