Campaigners have criticised "delays" in an investigation into the death of a man during the G20 protests a year ago.
Ian Tomlinson, 47, died after he was allegedly pushed to the ground by a police officer on 1 April 2009. Flowers have been laid at the spot in tribute.
In a letter to the director of public prosecutions (DPP) campaigners said the inquiry delays were "intolerable".
The DPP said he was working as quickly as he could on a careful investigation in "this difficult and complex case".
The petition letter to DPP Keir Starmer QC has been signed by several politicians, campaigners and members of the public.
It reads: "Ian's grieving family has been left in limbo for a year waiting for a full explanation about the circumstances of Ian's death.
"There is now very real concern as to whether the Crown Prosecution Service (CPS) proposes to charge anyone in respect of the assault and death.
"Delays in the investigation and charging decisions increase the suffering for families of victims, leaving them unable to gain closure and move on with their lives."
Family and supporters held a minute's silence in the City of London on Thursday, as well as laying flowers.
Speaking afterwards Paul King, Mr Tomlinson's son, said the family were deeply frustrated no decision had been taken on whether to charge the police officer at the centre of the controversy.
"It's been a long year, we just want justice."
During the G20 protests last year, an amateur cameraman filmed a policeman apparently pushing Mr Tomlinson to the ground. He collapsed and died shortly afterwards.
Mr Tomlinson was not a protester, but was walking home past the demonstration.
Mr Starmer said in a statement: "I readily accept the responsibility of the CPS to fulfil its duty regarding the investigation into the death of Ian Tomlinson.
"That investigation must be thorough, effective and impartial. And, I am afraid, in this particular case that means that it is taking longer than originally expected.
"As we have previously explained, the CPS and the IPCC are currently trying to obtain some further information. This relates to the expert medical evidence which is crucial to the proper determination of this case.
"Both the CPS and the IPCC are working as quickly as is compatible with a careful investigation in this difficult and complex case.
"But I acknowledge the frustration and anxiety that Mrs Tomlinson must be experiencing."
He said he would be writing to her.