The sixth teenage boy who was arrested on suspicion of the murder of a Polish man who was beaten to death in a suspected racial hate crime in Essex has been released on bail. Arkadiusz Jozwik, 40, died as a result of serious head injuries two days after he was attacked outside takeaway shops in Harlow on 27 August.

A 43-year-old man from Harlow, believed to be a friend of the factory worker and also from Poland, was also left with suspected fractures to his hands and bruising to his stomach following the unprovoked attack.

The brother of Jozwik believes the pair were targeted after a group of teenagers heard them speaking in Polish.

Police arrested four boys aged 15 and one aged 16 on suspicion of murder after Jozwik died from his injuries. All five were released on bail until 7 October.

A 15-year-old boy who was later arrested on suspicion of murder has now also been released on bail until the same date.

Speaking at the scene of the crime, the victim's brother, Radek Jozwik, said: "He was standing eating pizza and they picked on him because of that. He does not speak much English. The young teenagers are so aggressive.

"Parents need to speak with their children – they are out of control. One of the teenagers started and then seconds later there are 10 or 12 people attacking him. After the Brexit vote it has got worse – I have seen people change – it is hard at the moment."

The number of reported hate crimes in the UK soared by 400% in the wake of the EU Referendum on 23 June. According to figures released by the National Police Chiefs' Council (NPCC), there were 331 hate crime allegations in the UK in the week following the vote compared with the average of 63.

In July, a Polish family were sent a letter telling them to "go back to your f*****g country" after their garden shed was set on fire in an arson attack in Efford, Plymouth. A matter of days after the UK voted to leave the EU, laminated signs reading "Leave the EU/No more Polish vermin" were distributed around the Cambridgeshire town of Huntingdon, including four outside a school.

Speaking prior to the arrests, Essex Police detective inspector Al Pitcher said: "This was an extremely vicious and unprovoked attack.

"At this stage we are treating the assault as a potential hate crime but the motive remains unclear and we are continuing to keep an open mind. From our initial enquiries, we understand the victims were chatting and eating together when they were approached by a group of teenage boys.

"They were verbally abused before being assaulted and knocked unconscious."

Pitcher added: "This was a brutal assault and we are grateful for the public's support so far in coming forward with information to help us identify those responsible for this horrific incident and bring them to justice."

The Polish Embassy said the Ambassador Arkady Rzegocki will be visiting the town of Harlow to pay his respects to Jozwik. A spokesperson added: "We have been shocked by the murder of a Polish national in Harlow.

"Polish consul [have] conferred with local police in Essex. One of the lines of investigation is that of hate crime. We call on all witnesses to report to the police."