Alan Smith was home asleep on the living room floor between his two young children when his estranged wife was bludgeoned, stabbed and drowned in her bathtub two miles away, a Snohomish County judge was told Thursday.

Detectives and prosecutors have strung together “meaningless evidence” in an effort to pin the killing on her client, attorney Tiffany Mecca said.

However, evidence, including DNA found at the scene, points to an unknown assailant. Someone walked in through the front door, rummaged through Susann Smith’s purse, attacked her in the bedroom and then dragged her into the bathroom, Mecca told the judge.

“Alan Smith did not murder the mother of his children,” the public defender said.

Trial began Thursday for Smith with lawyers giving opening statements to Superior Court Judge Linda Krese. The jury box was empty. Earlier this week the defense team, in a surprise move, announced that their client was waiving a jury trial and requested Krese decide the case.

Smith is charged with first-degree murder for his wife’s February 2013 death. He faces decades behind bars if convicted. The trial is expected to last three weeks.

Snohomish County deputy prosecutor Craig Matheson on Thursday painted a picture of an angry man who meticulously planned his wife’s slaying.

Smith’s motive revolved around the couple’s ongoing divorce and custody dispute, Matheson said. The Smiths had been married since 2004 but the defendant filed for divorce in 2011 and moved out of the family home. It appeared to be a fairly routine divorce until the fall of 2012, when the Alan Smith “went off the rails,” Matheson said.

He became obsessed with the split, complaining that it was costing him thousands of dollars. Alan Smith, an engineer at Boeing, had been ordered to pay alimony and child support. The prosecutor told Krese that witnesses, including Smith’s coworkers, will testify that he frequently ranted about the divorce, his wife and how the court system was skewed to favor women. Smith told people he was afraid his wife would move the children out of the country. Susann Smith was a German national.

Alan Smith reportedly told an ex-girlfriend he wanted his wife to disappear and asked the woman how to make it happen without anyone knowing.

Smith began trying to convince the court that his wife was an unfit mother. A judge found there was no evidence to support his allegations.

“Seventeen days after that hearing Susann Smith was dead,” Matheson said.

The slain woman was last seen by a neighbor on Feb. 10, 2013. When she didn’t show up for her job in Seattle her coworkers called Bothell police. An officer, looking through a bedroom window, discovered a grisly scene: blood on the walls and bloody drag marks on the floor. Once inside officers found Susann Smith, 37, in the bathroom.

Krese was shown crime scene photographs.

Alan Smith, 39, on Thursday glanced up at the screen showing a photograph of his wife submerged in a bathtub. The water was red. The slain woman’s sister turned her head, avoiding the images.

Matheson explained to the judge that Susann Smith was repeatedly bludgeoned and stabbed, mostly in the head and neck. She had defensive wounds on her arms and hands. She was still alive when she was dragged into the bathtub.

The Snohomish County medical examiner concluded that she drowned.

Matheson detailed how investigators retraced Smith’s steps in the days leading up to the killing and the days after. They believe he rode his bicycle to his wife’s house from his apartment, less than two miles away. There is evidence that he wore gloves and disposable coveralls. His DNA is on a washcloth found under Susann Smith’s body. Bloody footprints in the house are consistent with Smith’s feet.

There is evidence that Smith planned to return to the house to remove evidence on Feb. 12, 2013, the day that his wife’s body was discovered, Matheson said. He left work early and bought a gas can, latex gloves, slip-on shoes, disposable coveralls and painter’s tape. The GPS on his car shows he drove to Bothell toward his wife’s home but turned around when he encountered a police barricade blocking off access to the house. He went back to work.

A search of his computer showed that Smith researched DNA evidence and also the cost of flights to Venezuela.

“This is no smoking gun but it certainly is curious,” Matheson said.

Then in June 2013, under the scrutiny of police and the increasing media attention surrounding his then girlfriend’s odd behavior, the defendant admitted he was responsible for killing his wife, the prosecutor said. Alan Smith reportedly made the confession to a man he met through church.

The defense had fought to keep the man’s testimony out of the trial, arguing that the conversation was protected because the man is a licensed minister. The man told detectives that he wasn’t acting as a clergyman when Smith allegedly made the statements. Krese ruled earlier that the man’s testimony was admissible.

Mecca cautioned Krese to reserve judgment on Smith’s alleged confession until the judge hears the circumstances surrounding the conversation between the men.

Prosecutors are ignoring evidence that Alan Smith isn’t the killer, Mecca said.

Detectives never found a murder weapon. It isn’t a surprise that his DNA was found in the house. He visited his children there on Wednesdays while his wife was at church choir practice. He had been there the weekend before her killing, helping his son in the bathroom, Mecca said.

Meanwhile, investigators found DNA in the house belonging to unknown people. DNA was found on Susann Smith’s wrist, where investigators expected to find the killer’s genetic fingerprint. The sample does not match Alan Smith or the people who removed her from the bathroom, the judge was told. There also is unidentified male DNA on the inside and outside of the front door, Mecca added.

“Just because they put these ideas together it doesn’t give them meaning,” she said.

The evidence is stacked against Alan Smith, Matheson said. He had the motive and voiced that motive repeatedly. He lied to detectives and forensic evidence links him to the scene. Most damning are his own words, the prosecutor said.

“There is zero doubt who killed Susann Smith,” Matheson added.