Mr Lyons described the dead teenager as a person of "immaculate character" and said he had been the "victim of an entirely unprovoked and vicious attack".
DCI Lyons said: "The youth, intent on violence, offered him [Jimmy] outside for a fight.
"Jimmy, being the type of man he is, declined that fight, and the aggressor was left outside the bakery.
"Not content with matters ending there, the youth then proceeded to smash down the door of the bakery, shattering the glass.
Jimmy's father: "He had an innate decency"
"He also picked up an advertising board and took it inside the bakery and wielded it around. A fight ensued and Jimmy received a fatal blow to his neck, cutting his throat with some glass.
Jimmy's parents, Margaret and Barry, who live in Lee, described their son who turned 16 on Friday, as "a wonderful boy".
Mrs Mizen said: "Jimmy was just the sweetest boy you could ever meet."
She said she had no anger for his killer. She said: "I feel for the parents of this boy.
"I don't know why, I can't get them out of my mind because what's happened to Jimmy is the worst thing possible, but we've got such wonderful memories.
"They haven't got wonderful memories for their son.
"All they can think about is the evil he's done. My prayers are with the family, that's all I can say. I can't, I don't feel anger."
Jimmy was attacked in a bakery
Earlier on Sunday, family and friends observed a two-minute silence outside Our Lady of Lourdes church, where Jimmy had been an altar boy.
They also laid flowers and read out messages of condolence near the spot where the attack happened.
Parish priest Father Edward Perera said: "There's a sense of numbness and devastation.
"We had over 400 people at the mass (on Sunday). And there wasn't a single person... who had a dry eye. Everybody was crying and weeping in the church."
Markus Ryan, Jimmy's head teacher at St Thomas Moore RC Secondary School said: "Jimmy was a very well liked, gentle student who always tried his best," he said.
"Our thoughts and prayers are with Jimmy and his family at this very sad time.
"We are holding a leavers' mass today as it will be the last time we will have our Year 11 students together in the school.
"St Thomas Moore has a very caring, compassionate school community and that mass will be dedicated to Jimmy and his family."
Jimmy is the 13th teenager to have been fatally attacked in London since the start of the year.
Speaking at the Global Day of Prayer at Millwall Football Club Mr Johnson said: "I want to say one very simple thing which is there are too many parents across London today who have lost their young children or young teenagers in the last year to gun crime and knife crime.
"Together we can do something and together we must do something and together we will do something."
During his campaign to become London's mayor, Boris Johnson pledged to make fighting youth crime one of his top priorities while in office.
LOCATIONS OF TEENAGE KILLINGS IN LONDON, 2008
(1) 1 January: Henry Bolombi, 17, stabbed, Edmonton, north London
(2) 5 January: Faridon Alizada, 18, stabbed, Erith, south-east London
(3) 21 January: Boduka Mudianga, 18, stabbed, Edmonton, north London
(4) 26 January: Fuad Buraleh, 19, beaten, West Ealing
(5) 19 February: Sunday Essiet, 15, stabbed, Woolwich, south-east London
(6) 23 February: Tung Le, 17, stabbed, Westminster, central London
(7) 29 February: Ofiyke Nmezu, 16, beaten, Enfield, north London
(8) 13 March: Michael Alexander Jones, 18, stabbed, Edmonton, north London
(9) 14 March: Nicholas Clarke, 19, shot, Brixton, south London
(10) 27 March: Devoe Roach, 17, stabbed, Stoke Newington, north London
(11) 27 March: Amro Elbadawi, 14, stabbed, Queen's Park, west London
(12) 3 May: Lyle Tulloch, 15, stabbed, Borough, south London
(13) 10 May: Jimmy Mizen, 16, Lee, south-east London
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