By Beth Germano

NEWTON (CBS) – A 24-year-old Waltham man is being held without bail after a clearer picture emerged in court of his violent confrontation with a Newton middle school boy. The 12-year-old was walking to his bus stop at Lexington and River Streets Monday when Carlos Cruz-Aguilar is accused of threatening him on the sidewalk.

“He made a demand of his cellphone and told the juvenile he knew where he lived and then he would kill him,” according to the prosecutor.

READ MORE: Mother Accused Of Putting Baby In Trash Can Charged With Attempted Murder
Carlos Cruz-Aguilar (WBZ-TV)

Carlos Cruz-Aguilar (WBZ-TV)

That’s when police say Cruz-Aguilar pulled out a kitchen knife and the two struggled. It was witnessed by Nick Rossi driving by at the time and thinking it was two boys rough-housing on a snowy day.

“They were on the sidewalk struggling. To me it was two kids playing around. But the thing that caught me off guard was it looked like the attacker threw the young boy onto the street and he almost got hit by a car,” said Rossi.

It wasn’t until news reports surfaced of the attack that he contacted Newton Police about what he saw.

READ MORE: Thieves Target Toyota Prius Catalytic Converters In Cambridge
Newton police released this sketch and photo of the suspected attacker. (Image credit: Newton Police)

Newton police released this sketch and photo of the suspected attacker. (Image credit: Newton Police)

Police released surveillance video of Cruz-Aguilar in a nearby Waltham Burger King wearing distinctive clothing with reflective bands. Police say he’s also seen with the boy’s cellphone sitting at a table trying to use it.

Carlos Cruz-Aguilar (WBZ-TV)

Carlos Cruz-Aguilar (WBZ-TV)

Within hours of the images going public police say they had him. An observant person spotted Cruz-Aguilar on Waltham Common wearing the pants and blue hoodie jacket she had just seen on the news. Police say he was intoxicated and noted he also matched the description.

At the station they say he refused to talk with detectives and asked for a doctor because he heard voices. Defense attorney Arthur Kelly says there’s an issue of competency, and Cruz-Aguilar will undergo a mental health evaluation before a dangerousness hearing on Monday.

MORE NEWS: Mitt Romney Taken To Hospital For 'A Lot Of Stitches' After Fall In Boston

WBZ NewsRadio 1030’s Kim Tunnicliffe reports

Beth Germano