Two Western Australian police constables who participated in the punitive expedition that led to the massacre, James St Jack and Denis Regan, were arrested and charged with murder.

The total number of victims of the punitive expedition led by St Jack and Regan is unclear, the highest being in the hundreds given by the brother of one of the participants in the massacre.

Over previous years, Frederick Hay had repeatedly taken and molested Aboriginal women with Gribble making complaints to authorities about his behaviour.

Constable James St Jack of the Western Australia Police based at Wyndham was directed to investigate this killing of cattle.

At dawn on 24 May, St Jack armed Windie Joe, Jacob, and Tommy with shotguns and the patrol rushed the camp to disperse the indigenous people.

Those who survived reported that many were injured and that two older men, Blui-Nua and Umbillie were killed by being beaten over the head with a stirrup iron or a rifle butt.

Without bothering to dress Hay gathered his clothes, mounted his horse and began to ride off but Lumbia grabbed a broken shovel spear and stabbed him in the back with it, killing him.

When Hay's body was found by the search party led by Constable St Jack, it had been largely consumed by predators and initially it could not be determined whether the remains were those of a white man or an Aboriginal person.

Although Regan was required to supply a written report accounting for every shot fired and to collect and return all used shell casings as proof, he never did so.

Upon hearing these reports, Sergeant Arthur Buckland, who was in charge of the Wyndham police, decided to recall the patrol and he left to rendezvous with them at the Forrest River mission.

When members of the patrol arrived at the mission for supplies, he informed them that the local Aboriginal people had told him that Lumbia had killed Hay.

Sergeant Buckland arrived at the mission on 24 June to recall the punitive expedition but as the police were now searching for a specific suspect, he allowed it to continue, albeit in a reduced form.

The police patrol now consisted of constables Regan and St Jack, accompanied by four Aboriginal trackers Mulga Jim, Frank, Windie Joe and Sulieman.

Constables St Jack and Regan took these prisoners to a nearby creek bed away from the police camp where they chained them to a tree and shot them dead.

They then burnt the prisoners' remains in a fire and dumped the resultant ashes and bone fragments in a shallow waterhole in the creek bed.

[3] While the punitive expedition was being conducted, various verbal reports of the killings were given by Aboriginal people to Gribble and by Murnane to the public at Wyndham when he opted out of the patrol.

[4] Additionally, Overheu's servant Tommy talked about the massacres he participated in to some bush Aboriginal people who passed on the story to Gribble.

[2] On 12 August Gribble, accompanied by Inspector E. C. Mitchell of the Western Australian Aborigines Department in Wyndham, visited two of the massacre sites at Mowerie and Gotegotemerrie.

Mitchell reported that he found considerable evidence of attempts to clean up the site and that he had recovered a quantity of intact human teeth and skull fragments from the ashes of a large fire nearby.

Mitchell sent a telegram to the Chief Protector, A. O. Neville:[5] Shocking revelations, saw place Forrest River, rocky higher bed where [... Aboriginal persons] chained small tree killed there then bodies burnt improvised oven.Two weeks later, the chief of police in the Kimberley region, Inspector William Douglas, personally conducted an extensive investigation of some of the massacre sites.

Douglas later sent other officers to investigate the massacre site at Dala where similar evidence of shooting, burning and dumping of human remains was found.

The Premier of Western Australia, Philip Collier, approved the creation of the Royal Commission to be overseen by George Tuttle Wood.

This 1927 Wood Royal Commission was tasked to investigate the killing and burning of bodies of Aboriginal people in the vicinity of the Forrest River Mission and the disappearance of key witnesses.

Wood was able to conduct part of the inquiry at the Forrest River region where he saw firsthand the Dala massacre site and was firmly convinced of the physical evidence he found there.

[3] On the recommendation of the Royal Commission, constables James St Jack and Denis Regan were arrested and charged in May 1927 with the murder of Boondung at the massacre site of Dala.

However, at a preliminary hearing, the case against St Jack and Regan was dismissed by Magistrate Alfred Kidson as he viewed the evidence as being "insufficient to justify its being placed before a jury".

[7] At the inquest into Hay's death on 3 August 1926, held in Wyndham courthouse, Lumbia was defended by Ernest Mitchell, Inspector of Aborigines in the North-West Department, who also served as interpreter.

[2] Constable James St Jack remained with the Western Australia police and was stationed at various places around the state including Perth, Kojonup, Bunbury and Carnarvon.

[2] Constable Denis Regan also remained with the Western Australia police and was posted to similar locations to St Jack including Perth and Kojonup.

Wood found that constables St Jack and Regan and other members of the patrol consistently lied to the commission to protect themselves and that they denied any killings despite the existence of written, verbal and physical evidence.