The state's case against accused serial killer Homer Lee Jackson III suffered a significant blow after a judge this month threw out his alleged confession, finding Portland police used improper and coercive tactics during more than seven hours of questioning over two days.

Police arrested Jackson, now 57, in October 2015 and accused him of strangling two teenagers and two women in their 20s who worked as prostitutes in the 1980s. He's pleaded not guilty to aggravated murder charges.

It's the latest setback in a case that has lingered for two years after police announced at a news conference that they had finally solved the asphyxiation deaths of four African American women who had been sexually assaulted and their bodies dumped. Relatives and friends of the women filled three rows in the courtroom's gallery when Jackson entered his plea.

Prosecutors and defense attorneys have been locked in a series of pitched court arguments about the quality of evidence in the case against Jackson, who was collecting disability payments and had lived quietly in a Northeast Portland for 13 years at the time of his arrest. He told court officials he was taking medication for paranoid schizophrenia.

Multnomah County Circuit Judge Michael A. Greenlick now has suppressed the two days of statements that Jackson made to two Portland cold case detectives when he was first taken into custody in October 2015, finding they were "made under the influence of fear produced by threats (and promises of leniency.)'' The judge cited more than a dozen examples from the interrogation.

At several points during the interview, Detectives Meredith Hopper and James Lawrence told Jackson that if he admitted to killing the women and explained why, they'd help him, he'd feel "great relief" and everything would turn out "for the best for everybody."

At other times, the detectives were hostile, exploiting Jackson's religious belief by suggesting God would never forgive him for his sins and promising that bad things would happen if he didn't start talking, the judge said.

Hours into the questioning on Oct. 15, 2015, Hopper advised Jackson not to put the families of his alleged victims through the pain of a trial. If he did, she told him, jurors would look at him as a monster because he couldn't remember how many women he killed.

The detectives would make sure he got the severest penalty if he didn't come clean on the killings, she said.

After Jackson continued to deny involvement, Hopper said, according to transcripts of the interrogation:

"Well then, you are a monster, my friend. You deserve what's coming to ya and I hope you get every bit of it. Because I think you're a nice guy to talk to, very pleasant, but I'm telling you right now, you are a monster and we will do everything we can to make sure you spend as much time in prison as we can put you there for. Because that's what's coming. You have the power to help these people."

The judge also highlighted Lawrence's likening of the case to a train as the detective urged Jackson to confess and "get on'' the train and then warned that if Jackson didn't, he'd get "run over'' by the train.

Conor Huseby, one of Jackson's defense lawyers, argued that the promises of leniency mixed with threats showed the detectives were trying to manipulate Jackson into confessing to murders "it was abundantly clear he had no memory of.''

State prosecutors countered that the detectives lawfully pressed Jackson about how he should clear his own conscience and give closure to the families of Essie Jackson, 23, killed in March 1983, Tonja Harry, 19, killed in July 1983, Angela Anderson, 14, killed in September 1983 and Latanga Watts, 29, killed in March 1987. Homer Jackson and Essie Jackson aren't related.

Jackson's statements were voluntary, and the detectives made no threats, the prosecutors said.

"There is simply nothing threatening about calling the defendant a monster nor is it threatening to tell the defendant that the detectives will work as hard as possible to do their jobs and make a strong case against the defendant in order to keep him in prison as long as possible,'' wrote Deputy District Attorney Susan O'Connor. "A threat must be more than expression by the officer of an intent to do something that the officer is authorized to do.''

The judge disagreed.

"Police threatening the worst punishment if convicted, I believe, is coercive," Greenlick ruled. Citing case law, he said police have the power to follow through on threats of harsher penalties and it's reasonable for a defendant to believe that could happen.

"Given the totality of circumstances, I believe the defendant could have started to believe that he would suffer a number of detrimental consequences, including that the judge and the jury would consider him to be a monster, the police would seek the longest possible penalties, the victims would be angry and influence prosecution negatively," the judge said. "It might also have been reasonable for him to believe that the interview might not end until he cooperated and he would not be able to let his family know what is going on."

Though the judge said he isn't required by law to determine whether he believed Jackson's statements were false or wrong, he called it "noteworthy" that Jackson admitted only to the killing of the 14-year-old yet had no recollection of what occurred and provided details that were inconsistent with how she died.

"It sure appears that the defendant became convinced that he committed murders for which he had no memory," Greenlick said.

"The fact that the defendant remembers Ms. Anderson or remembers being at a place where she took johns obviously does not mean that he committed murder on this particular date 34 years ago," he said.

Multnomah County Deputy District Attorney Jenna Plank argued that under recent case law, "the probable truth of a confession" shouldn't be a factor in deciding whether a statement can be admitted as evidence at trial.

The judge said he wasn't ruling on the truth of the statements. But he said he found in his close review of the interview with Jackson that the types of inducements or threats made by police can create a risk of an inaccurate admission.

"Backing that up is my concern the defendant isn't really able to come up with anything specific about any of these murders even though he seems to be trying," Greenlick said.

The judge threw out all of Jackson's statements to police after Lawrence, responding to Jackson who asked to call his sister during a smoke break on the first day of questioning, told Jackson that he couldn't call his sister until "we get to a point where we are working together on this."

Before that break, Jackson had repeatedly denied any involvement in the killings. After emerging from that break, he suddenly remembered "the girl in the house," referencing the death of Angela Anderson, the interrogation transcript shows.

The judge issued his ruling from the bench Oct. 2, but then sought more input from lawyers regarding an unusual turn in the interrogation, when police called Jackson's sister and allowed him to talk to her on speaker phone while the detectives listened and participated in the conversation.

When his sister asked why Jackson was there and why he was talking to police without a lawyer, he said, "I did it."

The judge ruled Tuesday that the unlawful police tactics tainted Jackson's admission to his sister as well, finding it reasonable for Jackson to believe at the time that "that the detectives would evaluate the statements he made to his sister and potentially react negatively to them.

Prosecutors haven't yet discussed with Oregon Department of Justice lawyers whether to appeal the judge's ruling to a higher court, Plank said Wednesday. "We're still moving forward,'' she added, noting there are hearings set next month on other pretrial motions in the case.

Prosecutors allege Jackson's DNA was found at three of the crime scenes. Jackson's lawyers have countered that his DNA isn't the only male DNA at the scenes and often was found in less suspicious places than the DNA of other potential suspects.

-- Maxine Bernstein

mbernstein@oregonian.com

503-221-8212

@maxoregonian