The report released Friday by police says 24-year-old Laura McQueen and Dominic Blackburn suffered blows to the head. The specific weapon has not been identified.
The bodies were found Wednesday in Blackburn's apartment.
"Laura was the most sweet, kind, loving woman in the world. Anyone who truly knew her would understand the beautiful heart and the love for people she truly had," said McQueen's sister, "Billie." "Dominic had this light in him and the ability, the moment anyone seen him, to bring a smile to everyone's face."
Prosecutors say McQueen's 27-year-old boyfriend is being investigated as a person of interest in the case.
No charges have been filed, but Daniel Edward Johnson appeared in court on Thursday to face a bail-jumping charge for an unrelated drug offense.
Inside a small viewing room, Johnson's father and stepmother sat side by side with McQueen's friends as a stoic Johnson walked into the courtroom.
Deputy Prosecutor Mac Setter asked for an extraordinary bail amount of $1 million, saying, "The defendant is a person of interest in double homicide being investigated by the Ferndale Police Department."
Johnson's father left the court without saying a word. But on Wednesday night, he told KOMO News his son had profound troubles, which leads him to fear for the worst.
"So many things going through my mind. There's anger, there's fear for my son, there's hurt for the family," he said.
Bob Johnson said he tried to turn in his son four months ago for his warrant in the drug case to no avail.
"If when I delivered him to the jailhouse, they had actually booked him when they had warrants, he would be off the streets and this wouldn't have happened. But that still doesn't excuse it," he said.