Mr Giannini was found dead in Manor Fields Park at 5am on Thursday, May 12, with a post-mortem examination later concluding that he died of a stab wound.
It is believed that the 34-year-old entered the park at 11.06pm but his movements up until his death are unknown.
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Now officers have released pictures taken from CCTV cameras near the park – and detectives want to speak to the people shown in the images.
All the pictures were captured around the park between 11.13pm and 3.09am on the night of the murder.
The senior investigating officer, Detective Chief Inspector Becky Hodgman, said: “It’s essential we build up a clear picture of the activity in and around the park on the night of the May 11 and into the early hours of May 12.
“We are looking to speak to those pictured as potential witnesses to the most serious of crimes. If you recognise yourself or someone you know in the images, please get in touch as soon as possible.”
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Two people have been arrested so far in connection with Mr Giannini’s death. A 17-year-old boy and an 18-year-old man are both currently on bail after being arrested on suspicion of murder.
If you have any information which could assist officers, contact 101 quoting incident number 122 of 12 May. You can also pass information directly to the incident room via https://mipp.police.uk/operation/14SY22K04-PO1.
Alternatively, contact Crimestoppers anonymously online via Crimestoppers-uk.org or by phone on 0800 555 111.