(AP) — Police arrested a total of six people in connection with a deadly explosion of illegal fireworks in a Honolulu neighborhood on New Year’s Eve and confiscated 500 pounds (227 kilograms) of unused fireworks from the scene of the blast, authorities said Thursday.

Police arrested two couples on Wednesday and one couple last Friday, said Honolulu police homicide Lt. Deena Thoemmes said. Police expect to arrest more people, she said.

Police were working with prosecutors to file charges but it is taking time due to the number of people arrested, large volume of evidence being examined and fireworks being tested, she said.

“We are recovering more evidence and identifying more individuals. As a result, additional arrests will be forthcoming,” Thoemmes said at a news conference.

The explosion killed three women, one man and a 3-year-old boy and injured about 20 others. The tragedy occurred when a lit bundle of mortar-style aerials tipped over and shot into crates of unlit fireworks, causing a rapid-fire series of blasts.

All six suspects were arrested on allegations of first-degree reckless endangering, first-degree endangering the welfare of a minor and multiple fireworks offenses. The first two suspects have been released pending investigation.

Manslaughter was the most serious potential charge in the case and was being investigated, Thoemmes said. Detectives will study how the fireworks were acquired and will ask the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives for help with that part of the investigation, she said.

The 500 pounds recovered from the scene were found in the carport and in vehicles belonging to people at the gathering, Thoemmes said.

The igniting of illegal fireworks — many of them aerials normally used in professional fireworks shows — has become increasingly common in Hawaii in recent years. People set off fireworks year-round but especially during the year-end holidays.

Hawaii authorities have said existing laws are difficult to enforce, in part because the evidence is often incinerated when fireworks are lit. Residents are also often reluctant to testify against their neighbors, making cases difficult to prove in court.

The deadly New Year’s explosion prompted Gov. Josh Green to propose overhauling fireworks enforcement laws, including creating $300 citations that police could issue to violators. He has also asked lawmakers to enable Class A felony charges and possibly decades in prison for those whose actions with fireworks severely injure or kill people.

The state Department of Law Enforcement has asked lawmakers to appropriate $5.2 million to hire eight people and expand a forensic lab to crack down on the persistent rampant smuggling of fireworks.

Police said the first two suspects arrested, a man and a woman both 33 years-old, ignited illegal fireworks at the New Year’s Eve gathering and allowed their children — ages 15, 10 and 1 — to also light illegal fireworks. The 1-year-old was injured, treated at a hospital and released, police said.

Thoemmes said the two other couples arrested Wednesday both lived at the house where the explosion occurred.

One couple — a 35-year-old man and a 38-year-old woman — allegedly attended the gathering with their four minor children. All four children were injured, taken to a hospital to be treated for their wounds and released.

The other couple was a 29-year-old woman and 32-year-old man. Police said they were at the party with their two minor children, who were not injured.

Thoemmes said some people initially interviewed by detectives provided false statements.

“Hindering prosecution is a crime and those who do so will face charges,” she said.