From the Daily Mail UK - former Royal Marine was enjoying a coffee when the attack occured...and he was armed:
Picture of former Royal Marine helping survivors and other photos of the incident are here: http://www.dailymail.co.uk/news/article-2430201/British-hero-mall-massacre-Ex-Royal-Marine-handgun-saved-100-lives-terrorists-ran-amok.html#ixzz2foanRPM0
...The former soldier is said to have returned to the building on a dozen occasions, despite intense gunfire.
A friend in Nairobi said: ‘What he did was so heroic. He was having coffee with friends when it happened.
‘He went back in 12 times and saved 100 people. Imagine going back in when you knew what was going on inside.’...