A bloody fingerprint. Surveillance footage. Threats made over the phone.

According to Boston police investigators, that is the evidence connecting 15-year-old Jose Hernandez to the murder of 18-year-old Blanca Lainez, who was found beaten and stabbed in an East Boston garage last month.

“We’ve seen extensive contact between this defendant and the victim,’’ said John Verner, an assistant district attorney for Suffolk County. “There is some argument between the two, and there are voice mails in which it appeared that this defendant is threatening Ms. Lainez.’’

Hernandez remained hidden during his arraignment Monday at East Boston Municipal Court, where he was ordered held without bail after pleading not guilty to a murder charge.

His arrest and arraignment came almost a month after Lainez’s body was found in a garage at a residence under construction at 54 Princeton St. She was on top of a bloodied pile of construction wood, her body bearing evidence of blunt-force injuries and stab wounds.

Investigators learned Hernandez and Lainez communicated extensively on social media platforms. Hernandez told police his nickname was “Smiley,’’ the same name used in the messages to Lainez, Verner said.

The text conversations suggested animosity between the two, according to a statement from Jake Wark, spokesman for Suffolk County District Attorney Daniel F. Conley.

The investigation of Lainez’s death is ongoing.

Authorities did not explain what caused the dispute between the teens.

With Lainez’s family in the courtroom, Verner read the police report that described how the combination of video and a fingerprint led to Hernandez’s arrest.

Investigators used security video from the area recorded the night of Lainez’s death to track the movements of a hooded male who left a home on Marion Street and walked toward the house under construction on Princeton Street, according to the report. Later that night, footage shows the male putting an object in his jacket pocket and running back toward the Marion Street home.

Hernandez, who was arrested June 30 for unlawfully carrying a 9-inch knife, told investigators he lived on Marion Street with a sister who is his guardian and other siblings.

During a crime scene investigation of the Princeton Street garage, police found a fingerprint on an unfinished wall that “had the presence of blood,’’ according to the report. Investigators matched that fingerprint to one found on Hernandez’s knife, Verner said.

Police arrested Hernandez on Sunday morning at the Marion Street home, the report said. Inside the residence police found a jacket that appeared to match the one worn by the person police had seen on the surveillance video.

Hernandez’s knife is being tested at a crime lab, Verner said.

Like Lainez, Hernandez is an immigrant from El Salvador. He is not a US citizen, and investigators told Verner they believe he could be deported. He was accompanied by a Spanish interpreter during his arraignment.

Lainez’s family, who told the Globe on Sunday that Hernandez’s arrest brought them toward closure, said they were upset they weren’t able to see the teen in person during the hearing.

“I wanted to see him, after hearing he was so young and having the capacity to take someone’s life,’’ said Susano Merino, Lainez’s brother, on Monday evening.

Relatives of Hernandez did not respond to requests for comment Monday.

His probable cause hearing is scheduled for Aug. 10.

John R. Ellement of the Globe staff contributed to this report. Miguel Otárola can be reached at miguel.otarola@globe.com. Follow him on Twitter at @motarola123.