Police believe the brutal stabbing death of an autistic 61-year-old man who spent some of his last minutes in his elderly mother’s arm picked the wrong person’s backpack off the street — thinking it was garbage — and was killed as a result.

Tyrone Padilla left his home on Creston Ave. near E. Fordham Road in Fordham at around 1:20 a.m. last Thursday, cops said.

Minutes later, video surveillance caught Padilla carrying a chair and backpack that police believed he picked up from the street, NYPD Chief of Detectives Joseph Kenny said at Tuesday a news briefing.

Among Padilla’s tendencies, he’s known to pick up what he believes is trash in front of and near the building, according to Kenny.

The victim was seen on camera being chased back into his building and into a second-floor stairwell where he was stabbed multiple times in his neck and torso.

The man’s 84-year-old mother Padilla’s mother heard a commotion outside and found her son bleeding on the stairs, relatives previously said in a tearful interview with the Daily News.

The horrified mother took her son into her arms before medics arrived and rushed him to St. Barnabas Hospital, where he died.

“This possibly could be that he picked up this person’s backpack by accident, which resulted in a confrontation, which resulted in the interaction in the staircase and he ends up being stabbed,” Kenny said.

A dagger with no blood was recovered at the scene, which police surmise may have belonged to Padilla, Kenny said.

The suspect took off on foot and fled to the Fordham Road station, where he hopped on a Manhattan-bound D train.

He is still being sought.