The next day she heard of the murder, and guessed that the Professor and his slave--for Cockatoo was little else--had rowed up to Pierside in a boat and there had strangled Sidney and stolen the mummy.

She saw Braddock and accused him.

The Professor had then opened the case, and had pretended astonishment when discovering the corpse of the man whom Cockatoo had strangled, as he knew perfectly well.
Braddock at first denied having been to Pierside, but Mrs.Jasher insisted that she would tell the police, so he was forced to make a clean breast of it to the woman.
"Now for it," said Random, settling himself to hear details of the crime, for he had often wondered how it had been executed.
"Braddock," read Archie from the confession, for Mrs.Jasher did not trouble herself with a polite prefix--"Braddock explained that when he received a letter from Sidney stating that he would have to remain with the mummy for a night in Pierside, he guessed that his treacherous assistant intended to effect the robbery.

It seems that Sidney by mistake had left behind the disguise in which he intended to escape.
Aware of this through me"-- Mrs.Jasher referred to herself--"he made Cockatoo assume the dress and row up the river to the Sailor's Rest.

The Kanaka easily could be mistaken for a woman, as he also, like Sidney, was slender and smooth-chinned.