A juvenile court judge on Wednesday heard arguments about whether a teenager who was 14 years old when he allegedly killed 68-year-old Susan Spiller during a home invasion should be tried as an adult.

During the adult certification hearing, a prosecution witness, Sara Sandhofer, a Hennepin County probation officer, testified that the case should be moved to criminal court based on several aggravating factors, including that the killing happened in Spiller's home and was carried out in a particularly gruesome manner. She also pointed to Spiller's age and slight stature.

"She wouldn't have been a match for many people," she told Hennepin County Judge Tanya Bransford, who was presiding over the hearing.

A reporter attended part of the testimony Wednesday before being asked to leave, because juvenile hearings are generally closed.

The defense will present its arguments against certification next month. The Star Tribune is not naming the defendant because he hasn't been charged as an adult.

Authorities still haven't said what motivated the teen, now 18, to allegedly break into Spiller's home in the 5100 block of N. Dupont Avenue sometime on the morning of July 16, 2015, and kill her before disappearing. Spiller had been strangled, beaten and stabbed so many times that medical examiners were unable to determine the exact cause of death, instead ruling that she had died of "complex violence."

Neighbors at the time told police that Spiller, a well-known community activist and artist, had been shaken by a confrontation she had the day before her death with a group of area kids after she called 911 on them for opening a fire hydrant near her house.

It is not clear whether the teen, whose family lived next door to Spiller, was among that group or if police ever considered him as a suspect soon after the slaying. Sometime after Spiller's death, his family moved to a northwest suburb.

His defenders say that before his arrest earlier this year, the teen had never been in trouble with the law and that he had been friendly with Spiller, with whom he would chat occasionally as she worked in her front yard.

For years, police had few leads in the case.

Detectives caught a break in the case last June when the suspect was arrested in Hennepin County on suspicion of threatening someone with what turned out to be a pellet gun. Since he was an adult, his fingerprints were entered into a statewide database, which police say turned up a match to prints found at the Spiller crime scene. Citing confidentiality requirements, authorities would not say what other evidence, if any, linked the teen to Spiller's killing.

He made his first court appearance on June 25.

Under state law, prosecutors can petition to transfer murder, rape and robbery defendants 16 and older to adult court, where sentences are often tougher.

Since 2000, 126 juveniles have been charged with murder in Minneapolis, according to records maintained by the county attorney's office.

No timetable has been announced for a decision in the certification proceedings.

Libor Jany • 612-673-4064 Twitter: @StribJany