Pippa Mills, Deputy Chief Constable of Essex Police, confirmed on Friday that four people have been arrested on suspicion of being involved in recent deaths of 39 people found in the back of a refrigerated truck.
She also called on media to stop speculating on the identities of those who died because "speculation is not helpful" and "may in fact hinder the investigation".
She urged journalists and those using social media not to speculate about the identities of the dead.
"We have officers working around the clock," she said.
The officer noted that a 48-year-old man from Northern Ireland was arrested on suspicion of conspiracy to engage in human trafficking and on suspicion of manslaughter.
A 38-year-old man and a 38-year-old woman from Warrington are in custody and are suspected of conspiracy to traffic humans and manslaughter. A 25-year-old man arrested on Wednesday on suspicion of murder remains in custody, she said.
Mills said, "(I am) acutely aware of international interest in this case, and we will provide more updates as we can."
She added, "I'd also like to make an appeal to anyone living illegally in this country who could help our investigation." And she urged anyone with information about the case to come forward and speak "without fear".
After the press briefing, Liu Xiaoming, China's ambassador to the UK, tweeted, "Our thoughts are with the 39 victims in Essex, no matter where they are from. This has again drawn world attention to the issue of illegal immigration. The world should join hands and take resolute measures to prevent such tragedy from happening again".
The Chinese Embassy team is working closely with Essex police, the Chinese Government attaches great importance to this horrendous tragedy. The relevant departments are mobilized and ready to cooperate with the British police with necessary assistance, he said in a separate tweet before the news conference.
